Manual Move Undo and Human vs Human Mode: See #202 #204

[dudecon]

Implements #204 with a new manual undo button at the top of the button UI Also implements #202 human vs human with thanks to @harrisi Both features are implemented together since undo rolls back 1 move in HvH, and 2 moves in HvB (the bot's last move, and the human's last move). Currently does not refund the thinkDuration spent calculating moves, since bots can cache calculation results. If refund is desired, we should probably store the think duration in the Move objects.