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.
Merge pull request #2352 from chris-allan/omeroweb-wsgi

OMERO.web WSGI additions