Allow map-placed frozen actors to start revealed.
Freeze civilian and map structures under fog. Fixes #3614.
Hide walls under fog.
Allow mods to set default lobby options.
Reset default state when a dedicated server clears.
Add lobby options for Shroud and Fog.
Tweak starting unit defaults.
Add RA starting units setup
Add trait interfaces for added/removed from world.
Rewrite bib to match new FrozenUnderFog capabilities.
Merge pull request #3633 from pchote/frozen-polish

Clean up loose ends with fog and lobby options.