Address Flask concurrency limitations

[danielsuo]

Eventually, we'll have to deal with this. Simple first option:

if __name__ == '__main__':
    app.run(threaded=True)
    # Alternately
    # app.run(processes=3)

Then, we could check out Flask deployment options. And of course we could stand up other things in front of Flask (e.g., gunicorn, elastic beanstalk).