Add volume control

[MorihiroS]

Is your feature request related to a problem? Please describe. It really frustrates me that you can't turn the music quieter when you're playing. If you turn down the overall sound, the sound of the effects becomes quiet too

Describe the solution you'd like Add a volume control at least for music, ideally separate for music, separate for effects

[thomasdn]

Seconded!

[MorihiroS]

@Hanmac, need keep label, pls