A little refresh of the UI

• Added Mic 1 control
• Removed some unused variables and implemented StreamController.close() as suggested by Dart Analysis
• Added window_size plugin and changed window title

No breaking changes here.
Just 4 new buttons that control where a channel output is going (headphones / speakers) and a new App Icon.

Disclaimer: Buttons and sliders work for how I set up my interface, your situation may be different.

Keep in mind that this app is structured to work based on my MOTU audio interface channels setup, so unless you have my exact setup it won't work as intended (it will control the wrong channels).
You can download it and try it yourself, it won't harm your interface of course.