add loaded region debugging to RegionManager
fix bad map panning when switching dimensions

accidentally set the default scale factor to 8.0 instead of 1.0.
optimize chunkToPixels colour blending

Modify chunkToPixels to use "front to back" alpha blending rather than
"back to front" blending.
With the back to front blending used previously the first opaque block
in the column needed to be found first so that the algorithm could blend
upwards from that point.
With front to back blending we can simply start at the topmost block and
blend until an opaque block is reached, so it saves a search through the
block column.
circular chunk lists for ChunkManager

Instead of using 64 "chunk buckets" and updating 1 bucket of chunks per
tick, now use a circular list of chunks and update a configurable number
of chunks per tick.

Revert MapTexture back to using a queue of rectangular areas for
updating the GL texture, rather than always updating entire regions at a
time.

Switch all ArrayList and HashMap instances to use the generic List and
Map interfaces.

Started testing out a recursive function for mapping only blocks in the
players line of sight in UndergroundMapRenderer.