Added autosaving of the current map. Autosaving happens in intervals when the map is changed. It will not overwrite the current map, but rather create new files, just like backups. Autosaving interval and number of files can be configured in the "Recovery" tab of the preferences. Autosaving can also be disabled there (not recommended). Autosaves will not have their nodes built for performance reason.

Fixed a problem where not selected geometry and things could not be dragged when the "don't move selection if any part of it is outside of map boundary" option was enabled

(Text labels are removed because of performance issues)

Added action to change the index of linedefs, things, sectors, and vertices. Can be accessed through a shortcut (not bound by default) or the menu of the respective mode (#903)

Fixed a regression where editing map elements did not preserve the selection order, but used the index order instead. Fixes #791

- editing a highlighted, not selected map element will deselect other selected map elements, then start editing the highlighted map element
- dragging a highlighted, not selected map element will deselect other selected map elements, then start dragging the highlighted map element
- dragging a single map element will keep its selection state. I.e. dragging a selected map element will not deselect it after dragging anymore
  - dragging a highlighted, not selected thing will not select it after dragging
- dragging a highlighted, not selected sector, while other sectors are selected, will only drag the highlighted sector, and not the selected sector (and deselect the selected sectors)

Linedefs Mode: fixed a problem where the "Select Single-sided only" and "Select Double-sided only" actions would still display the selection numbers of deselected linedefs

Linedefs Mode: fixed a crash that could happen when the mouse was moved out of the map control while an UDBScript was modifying the map

* Extended rendering options for drawing vertices
* Fixed vertex scale slider behaviour
* Force plot highlighted vertex in DragSectorsMode
* Moved ShouldRenderVertices property into the properties region
* made config file variable lower case to be in line with other config file variables

Snap selection to grid: fixed a problem that could cause a crash if geometry got removed by snapping it to the grid

Added map scripting capabilities to UDB (#656). Documentation at https://biwa.github.io/udbscript-docs/

Linedefs Mode: fixed a problem where flipping a highlighted linedef would also select the linedef. Fixes #571

Linedefs Mode: fixed a problem where after splitting a linedef the insert vertex preview would not work correctly
Vertices Mode: fixed a problem where after inserting a vertext the insert vertex preview would not work correctly

Linedefs Mode, Sectors Mode, Vertices Mode, Sound Environment Mode, Sound Propagation Mode: slightly improved performance when moving the mouse

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).

Removed lots of unnecessary casts to float of the Math methods. Also removed some other minor implicit casts

Added option to lock texture offsets of 3D floors when dragging the tagged sectors

Moved smart grid transform into Linedefs Mode and Vertices Mode, so it also works when simply highlighting a linedef or vertex. When doing smart grid transform on a linedef it'll also use the vertex closest to the mouse cursor as the origin instead of always the start vertex

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

* Mouse selection threshold

* Cleanup

* Fix selection bug

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.

Optimized map geometry merging performance when pasting map geometry.
Added, Curve Linedefs mode: added "Flip Curve" button.
Updater: partially rewrote fix from the previous commit.

Changed, Curve Linedefs mode: re-designed the mode UI. Alternative control options are now available (check Help tab while the mode is active).
Changed, Curve Linedefs mode: changed curve generation logic. Setting Distance to 0 will now divide selected linedefs into equal parts.
Changed, Curve Linedefs mode: curve vertices are now drawn.
Updated ZDoom_DECORATE.cfg.

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

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.

Changed: single-sided linedefs with only back sidedef present are now automatically flipped when loading a map.
Changed, "Flip Linedefs" action: the action will no longer flip single-sided linedefs with only front side.
Fixed a crash when trying to determine sprite angles when images with non-sprite names, starting with expected characters, were present in the Sprites namespace.