Replace cyclone-sse with socket.io

[tulku]

To reduce the number of parts (and data passing) of our system, we could replace cyclone-sse with gevent-socketio.
https://github.com/abourget/gevent-socketio
This has some advantages:

• Web Sockets are easier to debug, we can see the message in the client!
• We can use the socket for all communication client/server.
• There are working examples of gevent-socketio with Flask

We are already using gevent because of gunicorn.