Added code so that the links for Unstable Doors are handled properly by
DDTeleporter. Hurray! Also cleaned up some unused imports in the
BiomeGen classes and removed the RANDOM_DUNGEON link type - it was meant
for the dd-rift command but there is no need for it anymore.
Renamed MobObelisk to MobMonolith. Renamed LimboSkyProvider and
PocketProvider to have Xs at the ends of their names. This is temporary
so that I can change the name's capitalization. Windows considers the
names the same because it's file naming is case insensitive.
