[autoform] Make RelationField.fromcardinality a class method factory Instead of having the "RelationField" class hard-coded in this factory method (thus preventing any subclass to properly use it), we make that method a classmethod and instantiate the actual class instead of the base one.

.. -*- coding: utf-8 -*-


Server Architecture
-------------------

.. image:: images/server-class-diagram.png

`Diagramme ArgoUML`_

[FIXME]
Make a downloadable source of zargo file.

.. _`Diagramme ArgoUML`: cubicweb.zargo