Add support for controlling volume of applications that *occasionally* make a sound.

[DaddingtonPalace]

Some applications, like AisleRiot Solitaire, only occasionally make sounds. AisleRiot only makes sounds in response to a user initiated action (like dragging a card). I'll call this type of app an "occasional sound maker". Solitaire does not appear in the mixer list when I expand the menu. I presume (but have not verified) that this is because it is not making a sound at the time the menu is populated.

It would be very awesome were it possible to control the volume of occasional sound maker apps.
It might get tricky determining when to show/hide such an app in the menu. Maybe a simple solution would be to add support for listing such apps inside settings (like Application Filtering).

Thanks for a totally useful extension. Eeets lovely because eeets useful :)

[DaddingtonPalace]

BTW, looks like I'm using version 11 under Ubuntu 22.04.