Visual mode, 3d floors: sloped 3d floors are now always rendered as opaque (just like in GZDoom).
Fixed a crash when creating a new unknown thing (introduced in r2324).
Documentation: updated "Action Argument Settings" and "DECORATE keys" pages.
Fixed, Visual mode: floor brightness was calculated incorrectly when "Disable Light Effects"/"Restrict light inside" 3d floor flags were used and the floor had "lightfloor" property.
Fixed: "lightabsolute" flag was accessed incorrectly in previous commit.
Textures were not loaded properly from PK3/PK7 archives.
Visual mode: restored ability to remove textures using Delete action.
Visual mode: fixed several bugs in Cut/Copy/Paste things actions.
Visual mode: vavoom style 3d floors were not displayed properly.
Visual mode, 3d floors: added support for "RestrictLighting" (2) flag.
Visual mode, 3d floors: inner sides of 3d floors with "swimmable"/"render inside" flags used incorrect brightness value.
