Improved input handling in Qt Quick with focus on Touch and Mouse

There are several problems with input handling in Qt Quick, this task tries to collect the issues and proposals to solve them:

• event propagation:
  • flickabe in pinch area in flickable and similar nested hierarchies - events are moving towards parent items (stealing) but never back to children
  • the delivery code is rather complex - stealing, grabbers, touchgrabber vs mouse grabber...
• hover
  • fixes are in progress, but still worth mentioning here
  • several items hovered at the same time broken
  • when to stop propagating hover events (dialog on top)
• flickable
  • flicking several flickables at the same time is not possible since it's mouse based.