Fixed a problem where negative Y scales of sidedefs would result in a wrong offset when auto-aligning

Fixed a bug where flats on a 3D floor could not be auto-aligned (auto-aligning the flats of the tagged sector instead). Fixes #338.

Fixed an issue where selected objects were unnecessarily cleared in visual mode, resulting in slowdowns. Partly addresses #337.

Fixed: use application default font family for rendered labels if user-selected font is not available

- Fixed a bug where searching for generalized sector effects was not handled properly in Find & Replace Mode. Fixes 305.

- Auto-aligning textures now produces more intuitive results and is consistent between UDMF and non-UDMF maps

- Slope effects related to slope things are now displayed more correctly in visual mode (they were not applied at all). Fixes #160
- Slope effects of UDMF vertex heights are now displayed more correctly in visual mode (they could be overwritten by lower tier slopes)

- Unused textures error checker doesn't erroneously report textures on 3D floors with the use upper/lower flags set (followup to #269)
@ Refactored texture error checks to reuse code

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

- The missing textures checker now finds missing upper/lower textures on 3D floors when the appropriate flags of the Sector_Set3dFloor special are used. Fixes #269

- Textures will now wrap correctly in visual mode when the flag of the Line_SetIdentification special is set in Hexen format. Fixes #271

- Fixed a bug where the unknown texture error checker didn't report unknown textures on sidedefs that were never seen. Fixed #270

- Fixed a bug where moving the mouse outside the window could crash when pasting a selection while having auto dragging enabled. Fixes #110.

- Improved support for auto aligning scaled textures

3D floors are now updated in real time in visual mode when their control sector is sloped through the line slope action. Fixes #250.

* Adding check for missing activations on lines that have an activation-requiring action

* Adding skip check if the map isn't UDMF

* Oops, typo in name of check