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.
