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

Call RedrawSurface in OnRedrawDisplay of NodesViewerMode, SoundPropagationMode and SoundEnvironmentMode so that the map gets updated properly and not being stretched/squished when the windows is resized

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

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

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

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