This implements a structured user group model, propagating its changes
to vanilla Django groups. It features cycle detection at save-time,
although this cycle detection can only be seen as a fallback and forms
should check the acyclicity of their changes before committing using the
provided class method.
- Allows login via clipper.
- Default login method (django one) is still available.
- allauth allows user to change and reset his/her password, mails, social
accounts (clipper).
- Signup is managed through allauth.
