Return an error 401 instead of a 404 when session has timed out

Steps to reproduce:

1. In Web UI, navigate to a Folderish document (View tab)
2. Wait for session to expire (for quick testing, set session.timeout=1 in nuxeo.conf)
3. Navigate to User Settings > Authorized Applications (or any other tray menu item) from the left drawer items.

Expected result: nuxeo-expired-session ribbon is displayed along the top

Actual result: nuxeo-expired-session ribbon is NOT displayed along the top (only 404 message is displayed at page center)

NOTE: navigating back to nuxeo-app.html after the above triggers nuxeo-expired-session display as expected.

In Web UI, this would allow to display the ribbon when navigating to drawer items during an expired session.