Add Wagtail CMS for kfet app.

K-Fêt
- Integrate wagtail to serve "static" pages of old K-Fêt website
- Fixture "kfetcms/kfet_wagtail_17_05" contains a copy of old website
(as in May 2017).
- Media files can be got until end of June 17 at
http://partage.eleves.ens.fr//files/604e6dea2ceebc66b1936c6b3f911744/kfet_media.tar.gz

Login/logout
- Update package django_cas_ng to last version.
- Clean COFCASBackend.
- Change CAS version to 3 (version used on eleves.ens). This enables
the logout redirection (for CAS ofc).
- Add messages and clean existing ones on login/logout (for both
outsider and cas users).

Misc
- Update settings to bypass an incompability between debug-toolbar and
wagtailmenus packages.
- Better management of dev/test-specific urls (if debug-toolbar wasn't in
INSTALLED_APPS, media files were not served).
- UI improvements.

kfet/cms/management/commands/kfet_loadwagtail.py

@@ -0,0 +1,35 @@
+from django.contrib.auth.models import Group
+from django.core.management import call_command
+from django.core.management.base import BaseCommand
+
+from wagtail.wagtailcore.models import Page, Site
+
+
+class Command(BaseCommand):
+    help = "Importe des données pour Wagtail"
+
+    def add_arguments(self, parser):
+        parser.add_argument('--file', default='kfet_wagtail_17_05')
+
+    def handle(self, *args, **options):
+
+        self.stdout.write("Import des données wagtail")
+
+        # Nettoyage des données initiales posées par Wagtail dans la migration
+        # wagtailcore/0002
+
+        Group.objects.filter(name__in=('Moderators', 'Editors')).delete()
+
+        try:
+            homepage = Page.objects.get(
+                title="Welcome to your new Wagtail site!"
+            )
+            homepage.delete()
+            Site.objects.filter(root_page=homepage).delete()
+        except Page.DoesNotExist:
+            pass
+
+        # Import des données
+        # Par défaut, il s'agit d'une copie du site K-Fêt (17-05)
+
+        call_command('loaddata', options['file'])