Implemented UIGameBoard. (no tests yet)
The coupling here is a little higher than I would want.  The
playerpieces need reference to the view to make calls on movements, but
also need a reference to the graphics context of the UIGameBoard to draw
themselves.  Since they must draw after the UIGameBoard it makes sense
for the UIGameBoard to have reference to them so it can call each's draw
method after it draws itself.  Anyway, future refactor is likely.