Add flag to VisualActor for entities that should only be visible in Atlas. Patch by KareemErgawy. Fixes #1411.

git-svn-id: http://svn.wildfiregames.com/public/ps/trunk@13465 3db68df2-c116-0410-a063-a993310a9797
Merge remote-tracking branch 'remotes/trunk'