[server] add a db-namespace option in source definition (closes #1631339) "namespace" is preferred to the postgresql term "schema" to try and avoid confusion with cubicweb's schema. cubicweb now depends on logilab-database >= 1.13.0

Latest changes 
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* table of `all latest changes`_

Links below is providing useful RQL query example.

.. _all latest changes: view?rql=Any+M%2CX+WHERE+X+modification_date+M+ORDERBY+M+DESC+LIMIT+30