Add persistence and turn history

[edkim]

We need to add a database to store each game and its current state so that it can be loaded again.

In addition, we want to be able to keep track of every turn that has happened. There needs to be a "Turn History" (list) in the user interface that describes what happened during that turn. Clicking on a previous Turn in the History List will ask the user if they want revert back to that turn's board state.

The actual database provider can be anything you like (SQL-based, NoSQL).

This exercise is intentionally open-ended to allow the code contributor freedom to implement a sensible solution. That being said, if you have any clarifying questions, you can contact ed@socialtables.com