Added support for int8, int16, uint, uint8, and uint16 user variables

Draw slope mode: by default slope vertices are now placed with the left mouse button, and drawing a slope is finished with the right mouse button

This reverts commit 2e146309.

Stair sector builder: renamen "Single sectors" option to "Single steps". Added option to keep distinct sectors when using single steps

Using --- and +++ now also works correctly for the height offset in the edit sector properties dialog

Fixed an issue where the ZScript parser aborted with a cryptic error message when encountering a number that was too small or big. It now clamps the value to min/max for the data type and prints a warning

Fixed a bug where the wrong texture/flat with the same name would be displayed in the texture browser when they were loaded from a PK3 or directory

- 3D Floor Mode: fixed a bug where orphaned managed control sectors would be overwritten by relocating the control sectors

- 3D Floor Mode: removed non-functional "Spline" checkbox from the Edit Slope Vertex dialog

- Fixed a problem in the 3D floor mode plugin that caused an exception when saving the program preferences. Fixes #310.