[web] Move request handling logic into cubicweb application. (closes #2200684) We improve http status handling in the process: ``application.publish`` have been renamed to ``application.handle`` to better reflect it's roles. The request object gain a status_out attribute to convey the HTTP status of the response. WSGI and etwist code have been updated. Exception gain status attribute

     1

if not rql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',

     2

           ask_confirm=False):

     3

    rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',

     4

        ask_confirm=False)