Game option & rule implementation (2)

An option item is added to game menu. The option dialog will be set visible when player click the option menu item. There are three game options:

1. Show move hint - when player pick a piece, the board shows circles that indicate possible moves for the piece.
2. Rotate board - in order to give player a clear view, the board automatically rotates on y-axis with π angle after each move. This option is only valid when two players play the game.
3. Play sound - after player made a move, an action sound is played.

So far, rules for horse and chariot are done.