4 tasks given in the Assignment text file.

Change the getValidMoves method to have return type List<Integer> instead of int[].
Change the Board class to implement the Cloneable interface. The clone method must return
a deep copy.
Add a new player action Action.RESET that allows a player to reset the game to the initial
state.
Add a new player action Action.UNDO that allows a player to undo the last action.