Always handle 401 requests, except for network jobs

It is not enough to only implement it for the QNAM returned
by the ShibbolethCredentials, because we sometimes need it
when we have no valid credentials set (and are using dummy
credentials in the course).  The main use case is the
Webview opened by Shibboleth for FBA.

But as a side-effect, we can use it to handle auth requests
from the updater and other places.