Keep browser extension connection status up to date

[l0f3n]

Right now when a person joins the lobby, they will always be there even if they leave or gets disconnected. We could remedy this by continuously sending pings from the browser extension, and if the server has not seen a ping when it excepts it can send a player leave message to the client. This could also be sent in the case that a player leaves manually using the button.

[l0f3n]

We dont really want to remove such players from the graph, so one thing we could is mark them as inactive when they disconnect and kick all inactive players when the game starts. That way we never actually discard any interesting information about them. I think that would be a decent solution.