Hide specific app in the mixer

[duckimann]

Can we hide some app in a specific interface in the mixer? e.g. Discord. As you can see in my screenshot, there's 1 instance of it on every interface. But I'm using Voicemeeter to manage most of the IO so there's no need to show it in EarTrumpet.

I think we'll need a button to hide an app in the mixer and a tab in the settings to un-hide the hidden app (it should show which app is hidden on which interface).