Changed, Classic modes: bigger Thing arrows are now rendered when thing sprite rendering is skipped.
Changed, Classic modes: when "Fixed Things Scale" option is enabled, thing size stays at 2x scale instead of 1x when extra bounding box is rendered.
Added Preferences -> Appearance -> "Things transparency (Things mode)" slider.
Renamed Preferences -> Appearance -> "Things transparency" to "Things transparency (other modes)".
Externalized thing bounding box and arrow texture, used to render things in Classic modes (Textures/ThingTexture2D.png).
Updated ZDoom_DECORATE.cfg (A_SetUserVarFloat, A_SetUserArrayFloat).
Changed, Things mode: things are now rendered with a bit of transparency, so things beneath other things are now visible.
Fixed, Things mode: in some cases it was impossible to highlight a thing beneath other thing when their positions were the same.
Changed, 2D modes: changed thing bounding box and arrow image.
Fixed, cosmetic, 2D modes: in some cases thing arrows were rendered bigger than thing bounding boxes.
Map Analysis mode: selection color is now used when rendering affected things.
Fixed, Map Analysis mode, "Check unused things" check: checker returned false-positive results when used in Doom map format.
