Added config settings for the chance of generating a Rift Gateway in a
Nether Fortress. Also made it so that DD does not override Nether
Fortress generation if fortress gateways are disabled in some way.
Added a line in our config file for setting the block ID of Corium. Even
though it's only temporary code that's going to be removed later, people
need that to run our dev builds properly.
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
