[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

from os.path import join
from cubicweb.toolsutils import create_dir

option_renamed('pyro-application-id', 'pyro-instance-id')

create_dir(join(config.appdatahome, 'backup'))