Makes all actors selectable in Atlas and gives them selection rings (an
EditorOnly flag is used in the template for Atlas-only selectables).
Adds player colors to Atlas selection rings.
Fixes decal selection by falling back to old-style AABBs. Refs #1032.
Replaces UnitManager selections with EntitySelection helpers.
Adds DrawOverlays to Atlas views, for Atlas-specific rendering.
Fixes bug where selection rings conflicted with Move/rotate tool in
Atlas simulation test.
This was SVN commit r11177.