Add block colour save and load to file

Fixed dimensions other than overworld not displaying.
Fixed exception on saving map to image.
Fixed region code overwriting chunks and corrupting region files.
Changed chunk manager code to use the loaded chunk set to update the
map, rather than calling world.getChunkFromChunkCoords(x, z) for each
chunk.

Unfixed: Large circular map mode is stretched.
Unfixed: Regions sometimes don't load.