Adds a global connection state getter and connection events for follower quiddities

This exposes the get_connection_state switcher function to pyswitch as get_connections and adds a way to call it from the switcher server and swctl.

This also adds on_connected and on_disconnected as signals to quiddities so that a user program can be notified of connections and disconnections directly instead of having to rely on partial information relayed by the infotree.