Extended Chunks.proto to support lists of compressed and uncompressed chunks.
Chunks are now saved to disk using protobuf only. No java object serialization any more!

Note: Old worlds can still be loaded and are converted into the new storage format.

+ added additional decode() method to interface ProtobufHandler<T, M>
* updated file Chunks.proto to reflect latest changes in chunk storage
* updated class WorldRenderer to support the new storage format
* extended interface ChunkStore with new methods saveToFile(File) and loadFromFile(File)

* lots of changes to class ChunkStoreProtobuf to implement the new storage format
+ added support for threads monitoring to class ChunkStoreProtobuf
+ added subclass ProtobufHandler to class ChunkStoreProtobuf