Towards 1.13

[xoft]

Basic BlockArea implementation is done (PalettedBlockArea class), it supports getting and setting individual blocks, and pasting other BlockAreas. There's no merging yet, that will need a bit more thought about how to define the merging process. It should be sufficient to support rewriting the world storage, loader and generator to the new BlockArea now, so that's what I'll try next. Not sure if I'll need the BlockEntity and Entity storage added to the PBA class, that could complicate things a bit.