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.

cof/settings/dev.py

@@ -28,6 +28,26 @@ MEDIA_URL = '/media/'
 # Debug tool bar
 # ---
 
+# "Versions" panel of django-debug-toolbar <=1.8 is not compatible with
+# wagtailmenus.
+# See https://github.com/jazzband/django-debug-toolbar/issues/922
+# TODO: Bug should be fixed in ddt 1.9 (not released yet). When fixed, this
+# declaration may be removed.
+DEBUG_TOOLBAR_PANELS = [
+    'debug_toolbar.panels.timer.TimerPanel',
+    'debug_toolbar.panels.settings.SettingsPanel',
+    'debug_toolbar.panels.headers.HeadersPanel',
+    'debug_toolbar.panels.request.RequestPanel',
+    'debug_toolbar.panels.sql.SQLPanel',
+    'debug_toolbar.panels.staticfiles.StaticFilesPanel',
+    'debug_toolbar.panels.templates.TemplatesPanel',
+    'debug_toolbar.panels.cache.CachePanel',
+    'debug_toolbar.panels.signals.SignalsPanel',
+    'debug_toolbar.panels.logging.LoggingPanel',
+    'debug_toolbar.panels.redirects.RedirectsPanel',
+]
+
+
 def show_toolbar(request):
     """
     On ne veut pas la vérification de INTERNAL_IPS faite par la debug-toolbar