Visual mode, auto align textures: actually, it won't break anything if we vertical clamp texture offsets of a 3d floor sidedef while auto-aligning (this reverts a part of previous commit)...
Classic modes: event lines are drawn once again while panning the view (I've disabled this a while ago trying to fix performance problems in Classic modes).

Visual mode, auto align textures: vertical texture offsets of middle sidedefs are no longer clamped by texture height when said sidedefs are parts of 3d floor or are double-sided and not wrapped.

UDMF, Custom Fields: fixed a crash when trying to create undo snapshot for a custom field of type bool or string when the map's .dbs file is not present or it doesn't contain type info about said field.

Selection is now snapped to grid when pasted.

Visual mode: "Select adjacent walls with the same height" (Ctrl-Select) logic was not working properly in some cases.

Visual mode: offsets of double-sided middle textures were still clamped when not required in some cases.
Updated documentation.

Visual mode: added "Reset Local Texture Offsets (UDMF)" action (default key is Ctrl-Shift-R). It will reset upper/middle/lower texture offsets in UDMF and will act exactly as "Reset Texture Offsets" action in other map formats.

Default sector ceiling height can now be set in Preferences.
Default sector floor height can now be set in Preferences.
Maximum number of recent files can now be changed in Preferences.
UDMF, Custom fields: a warning is now shown when a user tries to manually add a managed filed.
UDMF: "Translucent" linedef flag is now marked as obsolete.

Sectors mode: effect and tag overlay can now be toggled separately from selection numbers.
Sectors mode: "View Tags and Effects" and "View Selection Numbering" settings are now saved to program configuration.
Sectors mode: removed "Lower Floor by 8 mp", "Raise Floor by 8 mp", "Lower Ceiling by 8 mp" and "Raise Ceiling by 8 mp" actions.
"Increase Brightness by 8" and "Decrease Brightness by 8" actions now work in Sectors mode.
Moved "Increase Brightness by 8" and "Decrease Brightness by 8" actions to "Edit" category. 
"Toggle Highlight" action now works in Sectors mode.
Moved "Toggle Highlight" action to "Tools" category.
Removed Brightness mode.
Updated documentation.

Sectors mode: sector tags are now shown on top of unselected sectors (works only if "View Selection Numbering" option is enabled).
Some cosmetic fixes here and there.

Sectors mode: selected and highlighted sectors are now highlighted in the same-ish way as in Visual mode.
Sectors mode: sector effect labels were not aligned properly.

Sectors mode: sector effects are now shown on top of unselected sectors (works only if "View Selection Numbering" option is enabled).
Updated documentation.

Fixed a crash when updating engine selector dropdown after removing engines when selected engine index was greater than engines count.
Some code simplifications in MapinfoParser, also it can now read fade/outsidefog color defined as "XXXXXX"

Visual mode: removed unrelated message when copying textures using "Copy Selection" action.

Added "Place Things" action (available in Sectors/Linedefs/Vertices menus). When used from Linedefs or Vertices mode, it will place things on top of vertices. When used from Sectors mode, it will place things inside of selected sectors.
Updated documentation.

Visual mode: added support for "fogdensity" and "outsidefogdensity" MAPINFO properties.
Sector Info panel now shows the number of sector's sidedefs as well as light and fade colors (UDMF only).
UDMF: Sector and sidedef flags are now copied/pasted when using "Copy Properties" and "Paste Properties" actions.
Fixed: in some cases default texture overrides were used even when corresponding option was disabled.
Sector Edit form: light and fade values were not saved when a value was pasted/entered into text box.
Sector Edit form: "reset value" button was not shown for light and fade values when selected sectors had different light/fade colors.
Reverted Open Map form changes from previous commit (my assumption that map marker is always empty was not correct...)
Updated documentation.

Snap Map Elements to Grid mode now works much faster and shows a message when completed.
Forced default textures are now only used in drawing modes.
Exception Dialog: long error descriptions were breaking window layout.
Map will no longer be shown in Open Map form if unrelated data is encountered inside of map namespace.

Manual linedef splitting: "Duplicate texture coordinates" and "Reset X coordinate, copy Y coordinate" settings now affect UDMF texture offsets.

Visual mode: added "Auto-align Textures to Selection (X)", "Auto-align Textures to Selection (Y)" and "Auto-align Textures to Selection (X and Y)" actions.
"Snap Map Elements to Grid" mode now tries to fix invalid geometry after vertex snapping.
Vertices mode: in some cases not all vertices were removed when deleting vertices.
Removed "Load GZDoom light definitions" from preferences. If you want to use GZDoom's GLDEFS definitions, add "lights.pk3" as a resource.
Visual mode: fixed a crash when toggling GZDoom Geometry Effects (Tab)
Fixed sector bounding box calculation error.
Renamed "Edit -> Grid Setup..." to "Edit -> Grid and Backdrop Setup..."
Updated documentation

Error Checking: renamed "Check unclosed sectors" to "Check invalid sectors". Now it also finds sectors with less than 3 sidedefs and sectors, which area is 0.

Changed the way sector bounding box is calculated. This fixes major slowdowns when a sector with invalid geometry (e.g. without triangulation) is highlighted in Classic modes and a crash in Visual mode when such sector is rendered.

Visual mode: fixed a crash when trying to move texture offsets of invisible sidedef.

Sector Info panel: in soma cases texture size was shown for unknown/missing textures.

Sector Edit forms: floor/ceiling textures can be cleared with right-click on texture selectors.