Fix mantis 3073: Additional Mainhall capabilities (from ngld)

Adds two new mainhall.tbl options:
1) "+Misc anim over doors:" (misc anim rendered after doors)
2) "+Cheat String:" (exchanges misc anim when cheat is entered)

git-svn-id: svn://svn.icculus.org/fs2open/trunk@10961 387891d4-d844-0410-90c0-e4c51a9137d3