Game layer built.  Game runs but statistics are spotty.
Found and fixed bugs from adding GBGame.  
Found an existing problem in GBScores; biomasshistory was declared as a
LinkedList but none of the routines that use it use an iterator.  That
makes it frightfully slow and it's being iterated a lot.  Changed it to
an ArrayList since some of the routines in question wouldn't adapt well
to an iterator.
Added game layer between GBWorld and the UI, moved scorekeeping and
tournament control to it.  

Implemented drawunderlay and drawoverlay in GBRobot.  Halos, radio
rings, and movement indicators are back!

Fixed several robot decorations that weren't drawing right.

Small performance enhancements in the Draw() routines, mainly about not
declaring unnecessary variables or recalculating values that never
change.