Add the ability to dim and mute outputs

[ttimpe]

trafficstars

It would be nice to be able to dim and mute monitor mixes from within the app.

[raduvarga]

It is theoretically possible, the only issue is that I don't own a Focusrite interface any more, and it is hard to test. I will see what I can do but it will be hard to test in the dark. I've made much more progress with the other similar app for Universal Audio, it can be tested without the physical device - there I already implemented the mute, solo, sends, etc., maybe you can take as inspiration.