401 logout

[KMnOFour]

Describe the bug
Need to handle notifying the user and logging out when the server returns a 401. Related to a prev ticket (?) to sync the session expiration with the backend. Timeout length needs review, and we need to cleanly handle edge cases, eg, where the browser has cached the session but the server has terminated it. You shouldn't get the 60 second resume session modal when you awaken an inactive chrome tab unless the server session really hasn't expired yet. In all cases, the ideal is for the resume modal to show in the last minute of the server session and at the client-side timeout intervals, and worst case, a notification forcing a logout should warn the user if the two are ever out of sync. Needs some analysis.