Change volume of non-default device when using keyboard volume buttons

[h7896v7347]

Hi,

I use HeSuVi with VB-Audio Virtual Cable to achieve HRIR 7.1 audio & equalizer

The default playback device (vb-cable) does not support volume control, you have to control it with a secondary device - Realtek Digital Output in my case (https://i.imgur.com/FUxGHlt.png)

Volume buttons on keyboard always control the default audio device. If there was an option to choose which device to control by default it would be great

Or alternatively add +/- x% option for rules in experimental version to assign other hotkeys for volume control( now there are only constant values for volume per device)

[h7896v7347]

#1084 - This is just what I needed! Works great in dev build.