It's cleaner anyway to use `tokio::broadcast::channel` than the list
of callbacks.
Also make it send pings only on long pauses between frames, as when
the camera is disconnected.
Users are often puzzled why there are short recordings. Previously
the only way to see this was to examine Moonfire's logs. This should
be a much better experience to find it right in the UI where you're
wondering, and without the potential the logs are gone.
Fixes#302
This gives much better information to the UI layer, getting rid of a
whole troubleshooting guide entry. See #119#132#218#219
I also restructured the code in anticipation of a new WebSocket event
stream (#40).
