Websocket connection to get currently playing

[aramperes]

Use-Case Description

A websocket API for getting live updates on what user(s) is/are listening to. This will help limiting polling to the API / rate-limiting issues.

Semantics

To prevent dead connections, we'll likely impose a limit on how many websocket connections a client ID or user can make.

Should support multiple users in the same websocket connection (with a reasonable limit on user count).