This commit fixes the issue of being able to scroll through the mixer
with the mouse wheel without modifying the volume slider. This
functionality can be temporarily restored by holding a click on the
volume meter.
Ignore wheelEvent using subclass
slider,spinbox,combobox with eventhandlers:
wheelEvent - ignore if widget is not focused,
leaveEvent - clear focus when mouse leaves event.
Use these new subclass widgets in properties
to ignore wheelEvent when scrolling.