Pop up prompt when user tries to exit main game

[puzzud]

Right now, pressing Exit in the Game state will immediately kill the state and return the user to the main menu.

Pressing Exit could be an accident. Therefore, we want to pop up a modal prompt dialog asking the user if they really want to exit the game. The user has the options of Yes or No.

In the case of Yes, the user is proceeded to the main menu (as usual).
In the case of No, the user is returned back to game play as the modal prompt is removed.

When the modal prompt is first displayed, a Game state method called setPaused is given the parameter "true". Similarly, when the prompt is removed, setPaused is called with the parameter "false". setPaused should be implemented and it should set a Game state member called paused to "true" or "false". However, that is the limit of this enhancement. It is up to the game logic to determine completely how setPaused behaves and how paused is observed.