Revert "turn() all pieces"

This reverts commit 3e3bb72bb6df397d317b14c35a2ac70e97921489.
Revert "Revert "turn() all pieces""

This reverts commit 1d148676478d4f645d2d9d541f94c29f3862eb35.
Updated Piece

GameBoard is no longer hidden from Piece. This is so that piece can
check if a spot is valid to move to each time that it want to move.