Editing modes: fixed some crashes related to undoing/redoing while objects with associations were highlighted

Improved associations and event lines. Refactorings to make the whole thing more sensible (hopefully). Options to display labels on event lines (can be configured in Preferences -> Editing).

Things Mode: performing the smart grid transform action will now set the grid origin to the selected or highlighted thing
Sectors Mode: performing the smart grid transform action will now reset the grid transform

- Added option to enable additive paint selecting without holding shift independently from regular additive selecting

* Mouse selection threshold

* Cleanup

* Fix selection bug

Fixed: inheritance from game configuration for dynamic lights; Fixed: visual representation of inherited lights (reported by Nash); Fixed: inherited thing arguments from game configuration; Added: //$ClearArgs for clearing inherited arguments.

* A direct tag-to-tag relationship can now be established between two things, which allows event lines to be properly setup between them. This is intended for interpolation and patrol specials which are linked via a shared tag, instead of an argument. A POSITIVE value represents the parent thing, where a NEGATIVE value represents the child thing.
* Added interpolation and patrol point specials to the persistent event line processing

Updated, Textures Browser: texture name length is now taken into account when calculating the width of texture items.
Internal: moved thing helper shapes creation logic from ThingsMode to LinksCollector.

Added, Things mode, Visual mode: added the ability to specify minimum/maximum argument range hint shapes using special DECORATE comments and Game Configuration properties (loosely based on range finder patch by Xabis).
Updated documentation ("Game Configuration - Action Argument Settings" and "DECORATE keys" pages).

Fixed, Script Editor: MD5 hash of text files stored in PK3 was calculated incorrectly, resulting in false warning messages when saving.

Added, Errors and Warnings window: most of warnings/errors related to (G)ZDoom text lump parsing can now be double-clicked to show warning/error source in the Script Editor.
Fixed: some map format conversion errors were never displayed, because errors list was cleared after performing map conversion.
Fixed: 3d floor indicators in 2D modes were not updated after leaving Visual mode.
Fixed: some UDMF-only interface buttons were never removed after converting map format from UDMF.

Fixed, Things mode: fixed a crash when deleting Light/Ambient Sound things when "Show Dynamic Light Radii" / "Show Ambient Sound Radii" settings were enabled.
Fixed: WAD lump index was not appended to lump name when reporting errors during ZDoom text lumps parsing.

Updated ZDoom_DECORATE.cfg.
Updated documentation ("Game Configuration - Sectors Settings" page).

Added, Things mode: sound radii are now shown for "Custom Ambient Sound" and "Custom Ambient Sound (no gravity)" things.

Added, Things mode: minimum/maximum sound radii can now be displayed for ZDoom's Ambient Sound things.
Added, Things mode: added "Show Light Radii" and "Show Sound Radii" main toolbar and View menu buttons.
Fixed, Action arguments control: invisible splitter between args1-3 and args4-5 is no longer draggable.
Updated ZDoom ACC (SetTranslation).
Updated ZDoom_ACS.cfg (SetTranslation).

Changed, Vertices/Linedefs/Sectors/Things modes: selected map element is no longer deselected after accepting Edit window when it was the only selected map element when the Edit window was opening.

Fixed, Things mode: thing selection labels must be updated when performing undo/redo.
Fixed another case of invalid sectors being created after dragging map elements when using "Merge Dragged Geometry" and "Replace with Dragged Geometry" drag modes.

Merged "Toggle models, dynamic lights and fog rendering" and "Toggle Geometry Effects" actions into "Toggle Enhanced Rendering Effects" action.
Removed "Dynamic light size" and "Dynamic light intensity" settings.
Updated documentation ("Rendering toolbar" page).

Added, DECORATE: added "//$ArgNRenderStyle" special comment. It allows to specify a rendering shape to display the value of given argument. Supported values are "circle" and "rectangle".
Added, DECORATE: added "//$ArgNRenderColor" special comment. It allows to specify a color used by the rendering shape.
Updated documentation.

Added, Visual mode: added support for FLATSPRITE, ROLLSPRITE, WALLSPRITE and DONTFLIP sprite rendering flags. Removed the older GLOOME-specific implementation.
Changed, "Align Things to Nearest Linedef" action: the action can now also align things with FLATSPRITE and WALLSPRITE flags (previously only things with attached models were aligned).
Changed, "Align Things to Nearest Linedef" action: the action can now align things to the middle part of double-sided linedef, if it has a middle texture assigned. 

Fixed: parts of UniFileds.UniValuesMatch() logic were inverted. In some cases this resulted in incorrect behavior of "Select Similar" action in UDMF map format.
Fixed, UDMF: alpha should be ignored when applying sector fade/light color gradients.
Ported eevee's fix for incorrect sector geometry occasionally created after dragging map elements (more info: https://github.com/sirjuddington/SLADE/issues/542).

Changed: "Unable to save the map: there are too many unique sidedefs!" error message now displays info about sidedefs counts before and after sidedef compression.
Fixed, Draw Grid mode: in some cases invalid geometry was created when drawing very large grids.
Fixed, Things mode, "Rotate Clockwise" action: fixed inability to change thing angle from 0 to 315 when "doomthingrotationangles" Game Configuration property was set to true.
Updated ZDoom_DECORATE.cfg.

Added "Split Joined Sectors" Edit menu item and toolbar button. When enabled, joined sectors adjacent to drawn lines will be split.
Added "doomthingrotationangles" Game Configuration property. When enabled, editor actions related to changing thing angle will snap the resulting angle to 45 degree increments. This property is set to true for vanilla game configurations.
Fixed a crash when changing game configuration from one without Thing actions support to one with them while in Things mode.
Fixed, cosmetic, DB2 bug: current editing mode button was deselected after reloading resources.
Updated documentation ("Game Configuration - Basic Settings" page).

Fixed, Things mode: fixed a crash when switching to Things mode when more than 256 things were selected.

Added: holding Control key while switching to/from Visual mode will now temporarily disable position synchronization (works only when 'Synchronize camera position between 2D and 3D modes' Preferences option is enabled).
Fixed severe lock-up after finishing dragging many vertices/linedefs/sectors in Classic modes.
Updated documentation ("Synchronizing camera position").

Updated ZDoom_DECORATE.cfg (ALLOWTHRUFLAGS flag).

Added, Drag Vertices\Linedefs\Sectors\Edit Selection modes: sidedefs facing outside of current selection are now reattached/added/removed after moving the selection.
Currently this will work as intended only if the selection ends up either completely inside a single sector or completely outside of any sector. Also this logic won't be applied if the selection contains the lines with only start or end vertex selected.
Internal: some TextLabel refactoring.

Added, Sectors, Linedefs, Things modes: map element selection order of rectangular selection is now direction-dependent.

Fixed, Visual mode, UDMF: in some cases Fade color was not applied to floor and ceiling surfaces of 3d floors.
Fixed, Visual mode: in some cases not all sidedef geometry was updated when updating sectors with Plane Align (181) action. Also fixed some more unnecessary geometry updates.
Fixed, Linedefs mode, Things mode: in some cases deleting linedefs/things caused a crash when trying to update text labels.
Fixed, Draw Lines mode: in some cases the drawing was prematurely finished when "Auto-finish drawing" option was enabled.

Added, Draw Lines mode: additional guidelines and horizontal/vertical line lengths can now be displayed for currently drawn line using "Show guidelines" top menu button.
Changed, Draw Lines mode: line angles are now shown only when "Show guidelines" mode is enabled.
Fixed, Draw Lines mode: in some cases "Snap to cardinal directions" mode was snapping only to diagonals.
Fixed, Draw Lines mode: snap to geometry behaved incorrectly when "Snap to cardinal directions" mode was enabled.
Changed, Things mode: dynamic light shape is now drawn using highlight color when a dynamic light thing is highlighted.
Added more sanity checks to MODELDEFS parser.

Added, Visual mode: "Increase/Decrease Scale", "Reset Texture Offsets" and "Reset Local Texture Offsets" actions now work when used on 3d floor sides.
Fixed: CVARINFO parser was unable to parse negative int/float values.
Fixed: in some cases TextLabel text size was checked before it was calculated. 
Internal, Visual mode: reduced the number of unnecessary geometry updates when changing map geometry.
Updated ZDoom_DECORATE.cfg (atan2 and VectorAngle).

MODELDEF parser: rewrote most of the parser logic. Now it picks actor model(s) based on Frame / FrameName properties.

Fixed, Things mode: in some cases selection labels were not updated after editing a thing.
Fixed, Things mode: selection labels were positioned incorrectly on things with FixedSize setting.
Fixed, Sectors mode: fixed a crash when selecting self-referencing sector when selection labels were enabled.
Fixed, Visual mode: in some cases Auto-align texture actions were not working when "use long texture names" Map Options setting was enabled.
Fixed, MD2/MD3 loader: available animation frames upper bound check was performed incorrectly, which would cause a crash in some very special cases.
Fixed, Game configurations: most Hexen/ZDoom teleport actions use TeleportDests as teleport targets, not MapSpots.

Added, Linedefs mode, Things mode: selection numbers can now be displayed and can be toggled using the "View Selection Numbering" mode toolbar button.
Added, Linedefs mode, Things mode: sector tags can now be displayed and can be toggled using the "View Sector Tags" mode toolbar button.
Fixed, Classic modes, DB2 bug: in some cases text label size was queried before it was calculated, resulting in text labels being rendered when they shouldn't.
Updated ZDoom_DECORATE.cfg (A_LogFloat).

Changed, Texture Browser window: "All" textures group is now saved/reselected like the rest of the texture groups when closing/opening the window.
Changed, Classic modes: bigger Thing arrows are now rendered when thing sprite rendering is skipped.
Changed, Classic modes: when "Fixed Things Scale" option is enabled, thing size stays at 2x scale instead of 1x when extra bounding box is rendered.
Added Preferences -> Appearance -> "Things transparency (Things mode)" slider.
Renamed Preferences -> Appearance -> "Things transparency" to "Things transparency (other modes)".
Externalized thing bounding box and arrow texture, used to render things in Classic modes (Textures/ThingTexture2D.png).
Updated ZDoom_DECORATE.cfg (A_SetUserVarFloat, A_SetUserArrayFloat).