Add wsgi.py for OMERO.web

Since Django 1.4 the wsgi.py has been included in all new Django
projects to ease integration with WSGI aware web servers.  Adding this
allows the alternative ways of deploying OMERO.web such as:
 * Gunicorn (http://gunicorn.org/)
 * uWSGI (http://uwsgi-docs.readthedocs.org/en/latest/)

As well as many others.  Static content serving is also supported in
multi-process mode with automatic restarts after changes.