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

Steps to reproduce:

1. Login to Nuxeo
2. Wait until session expires (for quick testing, set session.timeout=1 in nuxeo.conf)
3. Click either Administration or User Settings drawer items and access a tab in the opened menu.

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)

To continue observing the above behavior, perform the following steps after Step 3:

1. Click Nuxeo home icon in top left (observe session expired ribbon).
2. Refresh browser.
3. Repeat from Step 1 above.

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