Fixed Doors and Minor Dungeon Change

Fixed the regression bug that caused some of our doors to get placed in
the wrong direction. Changing doors to inherit from BaseDimDoor caused
BlockRotator to assume they weren't dimensional doors because it used
"instanceof DimensionalDoor" to check. Thanks for figuring it out,
Steven! ^_^

Also made a minor change to dungeon generation. We now check the game
rule doMobSpawning and don't spawn Monoliths from DungeonSchematic if
the value is false. This is useful for testing without Monoliths around.
We still do work to remove the portal frame blocks even if the mobs
aren't spawned.