Add a minimal implementation of the TicTacToe game engine

Add a minimal implementation of the TicTacToe game engine

This implements a /move endpoint to allow clients to send moves to the
server and an /events endpoint for the server to broadcast the moves
to all connected clients.

This TicTacToe class has some duplicated code from the empires Game
class. We should refactor this to have a common parent class to reduce
duplication.