Added concentric coloring

Can either of you think of a way to do this without passing a center to the concentric coloring method?
Restructured this a bit.  I split up colorConcentric into two methods (just for style), but didn't change the parameters.  I originally called the center location of the hexagons boardCenter, but in reality you can pass in any location on the board.  This should make that more clear.  Otherwise I think this is good to go.