Fixed the code for retrieving textures for ItemRiftBlade,
ItemRiftSignature, and ItemRiftRemover. Renamed Rift Blade item texture
again due to capitalization issues. Replaced World Thread texture with a
dark variant of MC's String - we can switch to another texture later.
Changed Rift Blade recipe to use Stable Fabric and a Blaze Rod. Changed
its base material from Gold to Diamond, which increases attack power and
decreases enchantability a little.
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
