Small changes to animation

Board draws last and changed bounce constant
Fleshed out abstract and human player

Still need to implement integration into the game classes
Added getColorAt method
Main player infrastructure

Player infrastructure is in place.  All that should be left is setting
up the dynamic between GameBoardWidget and ConnectFourGame in getting a
human player move and actually playing the game.  I'd also like to
animate a computer player move.  Definitely some kinks in there if I
want to avoid heavy coupling.  The line between the widget and game code
is getting fuzzy despite my efforts to keep them separate.  That should
be the last big hurdle before I can jump into the fun stuff.