Visual mode: added "Auto-align Textures to Selection (X)", "Auto-align...

Visual mode: added "Auto-align Textures to Selection (X)", "Auto-align Textures to Selection (Y)" and "Auto-align Textures to Selection (X and Y)" actions.
"Snap Map Elements to Grid" mode now tries to fix invalid geometry after vertex snapping.
Vertices mode: in some cases not all vertices were removed when deleting vertices.
Removed "Load GZDoom light definitions" from preferences. If you want to use GZDoom's GLDEFS definitions, add "lights.pk3" as a resource.
Visual mode: fixed a crash when toggling GZDoom Geometry Effects (Tab)
Fixed sector bounding box calculation error.
Renamed "Edit -> Grid Setup..." to "Edit -> Grid and Backdrop Setup..."
Updated documentation