Hide rubble in the fog of war except to the owner, so that other players don't see deleted buildings, especially civic center foundations.
Should use a special filter once the AI supports it (#4611), so that decorative rubble can be placed by maps too.
Differential Revision: https://code.wildfiregames.com/D635
Reviewed By: fatherbushido
Refs #3601 #3910 #3179