Draw Grid Mode: fixed a problem where "continuous drawing" would redraw all previously drawn shapes each time a drawing was finished. Fixes #912

UDBScript: fixed an issue where the Thing's class getSector method did not return null when the thing was not in a sector. Fixes #897

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)

The calls to native windows functions wouldn't be valid on any unix os
so expand the check.

The check for Windows XP is removed as that platform is not supported
anymore.

When saving a wad for the second time some code would run that tried to
use native windows function and caused a crash.

- A new "Show Textures" option up on the top bar, which draws any sector not flagged to be hidden on the textured automap
- Holding Shift will highlight sectors instead of lines
- Left-clicking on a highlighted sector will toggle the "Not shown on textured automap" flag
- Textures will be shown when Shift is held down even if the "Show Textures" toggle is off

Edit Selection Mode: fixed a problem where floor and ceiling textures were unintentionally scaled in UDMF when resizing the selection. Fixes #873

UDBScript: fixed a problem where floating point default script option values would be converted to the system's locale on hot reloading. Fixes #858

Nodes Viewer Mode: fixed a problem where trying to engage the mode with an empty map could crash. Fixes #857

Map Analysis Mode: fixed a problem where lines with fractional vertex positions could erroneously be reported as overlapping

Thing Edit Form (UDMF): fixed a problem where setting floating point values for health wasn't possible. Fixes #225

Stair Sector Builder Mode: fixed an issue where the number of sectors and the sector depth was not loaded correctly when a default prefab was set. Fixes #847

Nodes Viewer Mode: a crash that could happen when the nodes header was interpreted as an UTF-8 value should be fixed for good now (#827)

Improved performance in classic modes when panning the view. This is achieved by parallelizing plotting linedefs and vertices on multiple logical CPU cores. Enabled for linedefs by default. Disabled for vertices by default, since it can cause flickering when vertices are close to each other. Settings can be changed in Preferences -> Appearance

UDBScript: setting an UDMF string field to an empty string will not remove the field anymore, but actually set it to an empty string

Disabled visual sloping for game configurations that do not support plane equation slopes. Fixes #828
Added toasts for visual sloping events