Feature request: Volume control (e.g., mouse wheel)

[HubKing]

I wish I could change the volume within the player, not the system audio volume. It seems that the mouse wheel is currently doing nothing, so maybe it could use the wheel for controlling the volume.

Also, maybe in the Settings -> Output, I could set the default audio gain, because some sound fonts' volume is too low and some are too high.

[PolyMeilex]

Partialy addressed by audio gain setting of the buildin synth