Add support for horizontal mouse scroll wheel (eg. Win+MouseWheelLeft as shortcut for Volume-)

[WangTooNaive]

Hi! I really appriciate your dedication to develop such convenient software and I did my bit to support your awesome work on Steam. However, I've encountered an issue after switching to a mouse with a horizontal scroll wheel – Volume2 doesn't seem to support it. It would be greatly appreciated if the horizontal scroll wheel could be assigned as a shortcut, similar to the normal (vertical) wheel, eg. setting Win+MouseWheelLeft as shortcut for Volume- like Win+MouseWheelDown does. It would be even better to integrate horizontal mouse wheel into the "Rotating mouse wheel over Taskbar to change sound volume" function.

[irzyxa]

I added it for Hotkeys only. Will be available in version 1.1.9.466