[schema / sources] store data sources as cubicweb entities this implies several changes: * new CWSource / CWSourceHostConfig entity types * only the system sources and default admin login/password stored in sources file (other stuff will be ignored) * on startup, get sources definition from the database * every entities have a cw_source relation * a facet allow filtering

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"""%(distname)s views/forms/actions/components for web ui"""