1. Made World Thread available as dungeon loot
2. Removed useless config options for loot that doesn't appear anymore
3. Tweaked some config names and variable names for consistency
--Changed BlockRift to use ITileEntityProvider instead of BlockContainer
--Reorganized some of the code in TileEntityRift to improve performance
and readability
Changed rifts to using world.destroyBlock() instead of
world.setBlockToAir(). That has the advantage of causing block
destruction animations and sound effects instead of blocks vanishing
silently.
