To avoid all maps of world -> things, add a toWorldConfig method to ConfigPack which accepts a World as a parameter and creates a WorldConfig instance.

WorldConfig would build all world-dependent objects independently from the parent ConfigPack instance, and would be attached to a TerraWorld instead of a ConfigPack.

Advantages of this over old approach:

• No more world -> thing maps. This allows for
  • Better concurrency. No more needing to synchronize on these maps.
  • Better performance. This completely removes the need to get items from the several world maps in the config.
• Easier to understand code flow. Now, each world gets its own config instance, with a parent ConfigPack instead of all worlds on a particular pack sharing a pack instance.

Maps to eliminate:

• SamplerCache world -> Container map
• GeneratorBuilder world -> WorldGenerator map (this has the potential to significantly boost perf, this map is accessed a ton, this would completely remove the need to have it)
• UserDefinedCarver world -> CarverCache map