Add SeekController to the Smart Home API (in addition to Video)
The SeekController interface is currently only available for Video skills, whereas e.g. the PlaybackController interface is available for both Video and Smart Home skills. Saying 'go back 20 seconds' for a movie scene is a clear use of the interface, but this applies just as well to music (e.g. to repeat a guitar riff in a song). It may not be possible with streaming music but it can be done when controlling a media player playing local MP3 files so it would be a useful feature.