[sources] Simplify source's init method
Only call it when enabled instead of giving a boolean flag indicating whether it
is or not (which were not correctly considered).
.. -*- 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