CMS permissions can be managed from group views.

These permissions concern pages, images, documents and access to the
wagtail admin site. Only appropriate elements can be selected: only the
kfet root page and its descendants, same for the kfet root collection
(for images and documents), and kfet snippets (MemberTeam).

Add django-formset-js as dependency to help manipulate formsets.

K-Fêt groups created from "devdata" commands get suitable permissions
for the CMS.

kfet/cms/utils.py

@@ -0,0 +1,35 @@
+from django.apps import apps
+
+from wagtail.wagtailcore.models import Collection, Page
+
+
+def get_kfet_root_page():
+    """
+    Returns the K-Fêt root page, or 'None' if it does not exist.
+    """
+    from .models import KFetPage
+    return KFetPage.objects.first()
+
+
+def get_kfet_root_collection():
+    """
+    Returns the K-Fêt root collection, or 'None' if it does not exist.
+    """
+    return Collection.objects.filter(name='K-Fêt').first()
+
+
+def get_page_model_names():
+    """
+    Returns all model names of `Page` subclasses.
+
+    This uses the django apps registry (instead of `ContentType.objects.all()`)
+    in order to be usuable even before migrations are applied. E.g. this can be
+    used in `Field.__init__`.
+
+    Note these model names are the same in `model` attribute of `ContentType`
+    objects.
+    """
+    return [
+        model._meta.model_name
+        for model in apps.get_models() if issubclass(model, Page)
+    ]