Level providers are now cut back to just an interface to a world's data. They don't keep their own chunk registries or any stupid shit like that because the Level already does that.
This furthers the goal of being able to move level I/O off the main thread, and also drastically decreases the complication of implementing level providers.
The remaining methods, constants and fields in the NBT class now pertain to generic NBT functionality (except for the matchList()/matchTree() methods, but that's a job for another time). All NBT I/O specific logic has now been moved to NBTStream and its descendents.
Refactored level\format\generic\GenericChunk -> level\format\Chunk.
Re-added support for async chunk sending
Refactored most Level IO into new namespaces for more organisation
Removed LevelDB loader completely (will be re-added at a later date)
