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.

(cherry picked from commit 1544606bf0a883115e04f4409e3e2b30960dc1c9)

Conflicts:
	src/CMakeLists.txt
	src/creds/shibbolethcredentials.h
Fix backporting glitch the broke compilation