webui: add wsgi.py to be used with gunicorn in a production env
webui: add wsgi.py to be used with gunicorn in a production env

Former-commit-id: 00db0bef3c11360ebaa52c6691cff5235350c6ab
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine