Show how many people are watching a game

[kreibaum]

This requires me to track the "presence" in games. Then I'll be able to send stats about this presence to the frontend where it'll be rendered.

Take everyone that is present |> filter by "not a player" |> count.

[kreibaum]

I think having a separate in memory database that tracks websocket connections & users & rooms would be good. Gets rid of my ad-hoc data structures. But having separate databases doesn't work nice with sqlite. :-/