Fixed promoted pieces not moving on the screen.
Promoted pieces now draw in the correct place on the board.
Fixed castling (a few problems with getAllValidMoves, as well as assuming that compareTo would always return +/- 1). Still a problem with redrawing the rook in the correct place, which will require reworking recalculateCellSize.
Merge remote-tracking branch 'origin/master'
Made lots of minor fixes and improvements to how the graphics works, mostly to do with image loading.