Mass cleaning of kfet' authentication machinery

AccountBackend
- Should now work if used in AUTHENTICATION_BACKENDS settings.
- It does not retieve itself the password, as it should not be used
this way.

GenericBackend
- Delete useless 'username' arg of its 'authenticate()' method.
- Now delete the token in DB.

TemporaryAuthMiddleware
- New name of the middleware is more meaningful.
- Is now responsible to retrieve the password from the request, instead
of the AccountBackend.

GenericTeamToken model
- Add a manager' method to create token, avoiding possible error due to
unicity constraint.

GenericLoginView (authentication with the kfet generic user)
- Replace obscure system with a 100% HTTP handling.
- See comments for more information.

Misc
- More docstrings!
- More tests!
- Add some i18n.
- Add kfet/confirm_form.html template:
    Ask user to confirm sth via a form (which will send a POST request).
    Context variables:
        * title: the page title
        * confirm_url: action attribute for <form>
        * text: displayed confirmation text
- kfet.js : Add functions allowing to emit POST request from <a> tag.
- Non-link nav items from kfet navbar also get a 'title'.
- A utility has been found for the 'sunglasses' glyphicon!

kfet/auth/context_processors.py

@@ -1,7 +1,7 @@
 from django.contrib.auth.context_processors import PermWrapper
 
 
-def auth(request):
+def temporary_auth(request):
     if hasattr(request, 'real_user'):
         return {
             'user': request.real_user,