Setup flask-socketio for communicating between frontend and backend

[nathan815]

We'll use flask-socketio library to create a websocket server and respond to commands. This will allow us to send flight data to the front end in real time, while also making it easy to send commands to the backend.

Commands:

• [ ] flight.start - starts new flight, responds with new flight ID. Fails if flight already running.
• [x] flight.stop - stops currently running flight
• [ ] flight.info - gets info of currently running flight (ID, pilot, start time)
• [ ] flight.invalidate - marks flight as invalid for leaderboard (param: flight ID)
• [ ] flight.list - responds with list of previous flight ids, w/ pilot info
• [ ] joystick.list - responds with list of available joysticks
• [ ] joystick.select - selects a given joystick to use for flight (param: joystick index)

[nathan815]

I have put all the flask routes and socketio listeners in web/main.py. For now this will work fine, but we could always split it up later if needed.