Store the user's connected/disconnected status and display on the UI

This changes the code to store the connected/disconnected status of the user, and sends appropriate messages to the social API to display a different icon based on that status.

This is part of the work in https://trello.com/c/AeROD7cR. Note that the toolbar icon won't currently change dynamically due to bug 882132.

More status option displays are parts of different cards.