Implement the Bandscope

This is a more technical problem that it seems. The current code does not read any of the endpoint 4 packets. Another read/callback loop needs to be implemented for the bandscope to make it work. There probably also should be an instance or cousin of XTPandadapterMUX to handle the bandscope reading. This would make it such that you can tie multiple visual elements into the bandscope data if you wanted. Even a "bandscope waterfall" if that turns out to be helpful. As an aside, this notification architecture might work well for the audio too, which would allow for a rearchitecting of the system audio stuff.