tictactoe: Add a simple game-info div

tictactoe: Add a simple game-info div

This is populated dynamically by the server sending the game-info
event and contains both the game ID as well as the URL.

We're not yet doing any interesting styling here, (it should get
tucked up into the upper-left corner as just a button with the game
ID, and when clicked on it will expand to show the URL to share).