Do basic HTTP authentication using QNetworkAccessManager, not manually

Review Request #109504 - Created March 15, 2013 and submitted - Latest diff uploaded

Sven Brauch
Until now, attica wrote the credentials into the URL and into the header
on every request as soon as the user had entered them.
This could lead to warning dialogs from the HTTP kioslave about
possible address spoofing, since credentials must only be sent if the
server requests them explicitly. I noticed this when writing my own OCS server;
please don't ask me why it even works for opendesktop ;) Possibly it has to do with
the SSL encryption they use.
This patch changes attica to use the "official" way to supply credentials, which is
connecting to the signal the QNetworkAccessManager procides, and filling in
the credentials there.
To keep this change as local as possible, the credentials are stored in
the User attribute fields of the QNetworkRequest, because then they
can be both set and read in one central place.
Manual testing.