Add the barest template of an implementation of a tictactoe game

This supports only the ability to select a nickname (which is provided
by lmno.js), and then the serving of minimal HTML into which the
tictactoe React cient can render itself.

There is not yet here any implementation of API endpoints specific to
the tictactoe game. Those will have to come later. (So, for now, each
player that joins a game of Tic Tac Toe will have an independent game
without any communication between them.)