Add a wsgi application factory suitable for wsgi servers.
This factory can generate a wsgi application for a cubicweb instance.
It reads the instance name from the CW_INSTANCE environment variable, and
activates the debugmode if CW_DEBUG is defined in environment.
It is usable by uwsgi as the 'module' parameter :
CW_INSTANCE=test uwsgi --plugins python,http --http 0.0.0.0:8080 --module pyramid_cubicweb:wsgi_application()