Fix issues with multiprocessing

Gevent conflicts with multiprocessing and threading.

We have already changed all gevent-dependent code everywhere but in __main__.py, because we need a production-ready WSGI server.

Some options are: tornado, uswgi and gunicorn. Unfortunately, if we go the uwsgi or gunicorn way we would need to use subprocess to start the server, or do without the command and simply a gunicorn script.