For the "ignore wheel" widgets, do not leave focus on mouse leave
events. This causes unintended side effects such as not being able to
type in edit boxes, and is very annoying.
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.