Edit Selection Mode, Flat Align Mode: fixed a bug where snapping occurred to wrong positions on lines when the grid was transformed

Draw Rectangle Mode: fixed a problem where the guidelines were not displayed correctly under certain conditions

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

Vertices Mode: the preview vertex is now correctly shown on intersections between the closest line and the transformed grid

Added some error handling to duplicating 3D floors

Changed how performing undo interacts with volatile modes (it will now actually perform the undo instead of just canceling the volatile mode)

- Added preliminary code to remove new 3D floor control sectors when pasting was canceled after duplicating 3D floors

Added functionality to duplicate 3D floor control sectors of selected sectors and paste selected sectors with the new control sectors assigned

3D Floor Mode: fixed a bug with the "Detach all" and "Split all" that would create (and immediately delete) redundant control sectors

Draw Grid Mode: added option to to draw the slices relative to the origin of the drawing (so that you don't have to change the slice interpolation all the time)

Added the "nocount" UDMF thing flag (as "No completion count") that was added in GZDoom 4.4.0 to the ZDoom config. Fixes #422.

Added comments to code

Made sloping work more reliably with irregularly shaped sectors

3D floor mode: fixed a problem where splitting a 3D floor didn't work correctly when some selected sectors didn't belong to that 3D floor

Improved handling of changing input boxes in slope arching form

Texture sets now work with textures from a directory or PK3/PK7 (it matches against the short 8 character name)

Improved functionality

3D Floor Mode: fixed a bug that would not increment the sector tags correctly if a tag range is used

Fixed a bug where modifying a user_ ZScript variable through the custom properties tab would cause a crash. Fixes #420.

Edit Selection Mode: fixed a bug where the control sectors of sloped 3D floors were not updated correctly when one 3D floor was applied to multiple sectors