Add a simple tictactoe game, implemented with React

Add a simple tictactoe game, implemented with React

This isn't a proper LMNO game, (it's not networked at all), but it's a
starting point for seeing how we might structure a React-based client
(and we can develop this into a proper LMNO game).

In fact, the source code here came directly from the React tutorial
here:

	https://reactjs.org/tutorial/tutorial.html

Note that I've not pulled in the 1000+ npm modules that would have
come from using create-react-app as recommended in that tutorial. As
can be seen here, by example, none of them are needed. The only build
tool requireed is something to compile JSX and we've got that working
via the Debian-provided babel packages (as seen in the most recent
commits here).