adding who-is-online display (last_seen_activities).

User.last_seen_activities
User.update_last_seen_activity('is eating lunch', lunch_object)
User.update_last_seen_activity(nil)  # on logout

LastSeenActivity.current  # 5 mins

trello: https://trello.com/c/51DTx3aY/659-wer-ist-online-anzeige