Add integration tests for games played between two users
Change `UIPort`’s `moveWasMade` to `makeMove`
Add PlayerType enumeration and Player struct
Use players rather than tokens; add GameProtocol and MockGame
Switch tokens when `Game`’s `move` is called
Add MockAIPlayer and integration test for game between a user and an AI
Add `MinimaxPlayer`
Handle AI service being down; refactor like mad