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/middleware.py

@@ -1,12 +1,13 @@
 # -*- coding: utf-8 -*-
+from django.contrib.auth import get_user_model
 
-from django.contrib.auth.models import User
+from .backends import AccountBackend
 
-from .backends import KFetBackend
+User = get_user_model()
 
 
-class KFetAuthenticationMiddleware(object):
-    """Authenticate another user for this request if KFetBackend succeeds.
+class TemporaryAuthMiddleware:
+    """Authenticate another user for this request if AccountBackend succeeds.
 
     By the way, if a user is authenticated, we refresh its from db to add
     values from CofProfile and Account of this user.
@@ -15,15 +16,23 @@ class KFetAuthenticationMiddleware(object):
     def process_request(self, request):
         if request.user.is_authenticated():
             # avoid multiple db accesses in views and templates
-            user_pk = request.user.pk
             request.user = (
                 User.objects
                 .select_related('profile__account_kfet')
-                .get(pk=user_pk)
+                .get(pk=request.user.pk)
             )
 
-        kfet_backend = KFetBackend()
-        temp_request_user = kfet_backend.authenticate(request)
+        temp_request_user = AccountBackend().authenticate(
+            request,
+            kfet_password=self.get_kfet_password(request),
+        )
+
         if temp_request_user:
             request.real_user = request.user
             request.user = temp_request_user
+
+    def get_kfet_password(self, request):
+        return (
+            request.META.get('HTTP_KFETPASSWORD') or
+            request.POST.get('KFETPASSWORD')
+        )