added ChunkChangeObserver

WDL gets changed chunks from VoxelMap (if and only if it exists), allowing both to use isChanged
Also updated to some more recent MCPtest mappings

First two commits are the observer changes, and stubs for voxelmap against which to compile.  

Because I suck at Git, the third commit is completely separate, and represents a drop-in liteloader replacement for all the base class edits (which is slightly redundant, given that I have since discovered someone else has created the same thing)