Changed DDLoot to use the correct item IDs when adding DD items to
chests. Moved loot chest registration from init() to postInit() in the
hopes that we'll be able to catch the loot of other mods that also hook
into Vanilla chests.
Dimensional dungeon loot chests are now registered with Forge. Other
mods can tap into our chests and our own generation is cleaner. The list
of items in our chests is generated in DDLoot.