[Phoenix] Authentication handling rewrite complete

[Andreas Wuest]

Hi

My reimplementation of the authentication handling is basically 
complete. Authentication handling is completely transparent now and only 
a boolean flag away. When using the network service, you can simply set 
a flag which indicates that the network service should handle 
authentication automatically upon the receipt of a 401 response, if a 
suitable module to handle the requested authentication scheme is available.

This means that whenever you issue a network request, you will always 
get back either the requested document, or an error if something went 
wrong, or no suitable authentication handler was found. Before, you had 
to handle authentication yourself at every callsite, and then reissue 
your original request after a successful login.

We now have the opportunity to protect virtually everything using 
Neutron-Auth, from Neutron documents and NARs to Atom entries and even 
Atom feeds.

If desired, I could even convert the Neutron introspection and the APP 
service document fetcher to use the network service, thereby enabling 
protection of those resources via Neutron-Auth as well.

Furthermore, the error handling has been vastly improved. Unfortunately, 
this means that the whole thing might look a bit rough right now at the 
UI level, because you are getting much more feedback. Therefore, please 
tell me if you feel that there is a bit too much feedback, and how it 
could be improved to not confuse the user.

What's left: I still need to remove some now-obsolete code. Also, I'm 
going to introduce an expressive exception hierarchy which enables the 
UI to better distinguish between feedback that should be shown to the 
user or not, and if it is being shown, to i18n it.

-- 
Kind regards,
Andi