Demonstrate driving time machine from a progress bar / slider on a notification.

[rjrjr]

Inspired by https://www.androidpolice.com/2019/09/09/spotify-seekable-audio-progress-bar/

May have to do custom layout b/c this is media specific

[zach-klippenstein]

I think we might be able to just use MediaSession for this even though we're not actually playing any media… need to look at the API more.