HW11 AI: final submission:
(1). Add simple AI
(2). Remove the "Finish This Round" Button.
(3). Fix the bug for landing piece out of the yellow square.
(4). Instruction for test:
	(4.1). Game URL:
http://7-dot-abalone-game-smg.appspot.com/AbaloneGame.html
	(4.2). GWT Emulator URL: 
	http://6.smg-gwt-emulator.appspot.com/
	(4.3). Set "Network Delay" to be 500 when testing to make the animation
smooth and clear