Implement websocket API

[amorphic]

We've decided to base Braubuddy on a websocket API. We still need to determine:

• Which (if any) framework to use.
• Which protocol to use.
• Whether or not the uPython version of Braubuddy can use the same framework and packages as the standard Python version.

Use the answers to these ---^ questions to implement a websocket API with a basic get_status endpoint.

[amorphic]

Potential frameworks (all of these use asyncio and provide native websocket support):

• sanic
• tornado
• aiohttp
• responder

@sjdines FYI the latest episode of Talk Python To Me is with one of the Sanic maintainters. Worth a listen.

Consideration factors I can think of:

• Available plugins/libs (for things like our protocol of choice)
• Documentation
• Community
• Interface (sanic, aiohttp and responder all roughly emulate flask, tornado has its own thing it's been doing for a while).
• Any possibility of running in uPython environment (not holding my breath)
• Potential for nicely integrating frontend SPA into builds (e.g. this in Responder).