Global Tic-Tac-Toe state

[ethanl21]

The state of the TicTacToe game should be global so it is not lost when transitioning to and from the its scene.

Tasks include:

• Track the TicTacToe game's state in a singleton

Definition of done includes:

• Both players (user and AI) can claim squares on the TicTacToe board, depending on the RoundState
• When transitioning to an in-progress tic-tac-toe game, the previous marked squares are indicated

I don't anticipate that this task will be blocked by anything in particular.

[Kynot54]

Done, there are other debugging issues that I've noted and will list as separate issues