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!

cof/settings/common.py

@@ -100,7 +100,7 @@ MIDDLEWARE_CLASSES = [
     'django.middleware.csrf.CsrfViewMiddleware',
     'django.contrib.auth.middleware.AuthenticationMiddleware',
     'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
-    'kfet.auth.middleware.KFetAuthenticationMiddleware',
+    'kfet.auth.middleware.TemporaryAuthMiddleware',
     'django.contrib.messages.middleware.MessageMiddleware',
     'django.middleware.clickjacking.XFrameOptionsMiddleware',
     'django.middleware.security.SecurityMiddleware',
@@ -128,7 +128,7 @@ TEMPLATES = [
                 'wagtailmenus.context_processors.wagtailmenus',
                 'djconfig.context_processors.config',
                 'gestioncof.shared.context_processor',
-                'kfet.auth.context_processors.auth',
+                'kfet.auth.context_processors.temporary_auth',
                 'kfet.context_processors.config',
             ],
         },
@@ -191,7 +191,7 @@ CAS_EMAIL_FORMAT = "%s@clipper.ens.fr"
 AUTHENTICATION_BACKENDS = (
     'django.contrib.auth.backends.ModelBackend',
     'gestioncof.shared.COFCASBackend',
-    'kfet.auth.backends.GenericTeamBackend',
+    'kfet.auth.backends.GenericBackend',
 )
 
 RECAPTCHA_USE_SSL = True