Change isometric rotation so northwest is at the top by default

Since we need to start isometric renders from the top corner, it just
makes sense to have the minimum X and Z values in the top corner instead
of the left.

Also, world image will now skip null region images instead of aborting.
Neighbours, and shadows/highlights seem to work for orthographic maps

Chunks and regions can now read block info from their neighbours.

This means we can now draw highlights and shadows.

Next we'll find a way to use neighbour information to improve
isometric maps.