Disconnect stale connections

[osks]

Implement a way to disconnect stale connections. I think it would be good enough to say that a connection gets disconnected after ~2 weeks idle time. (The exact time isn't that important, but I'd like it to be at least one week.)

See osks/jskom#41

[osks]

Another feature on this topic is to make it possible to use the same session from multiple browsers. The idea: When a user successfully logs in to a LysKOM server, list the user's other sessions (from the same httpkom instance), if there are any, and allow the user to use one of those sessions instead of the newly created one. If the user decides to use an old session, the newly created session is disconnected immediately. The user could also be presented with the possibility to disconnect the other session(s).

This would allow users to see if they already active sessions, and make it possible to avoid stale sessions, even if a connection ID is lost.