title: Zoom Flickable's content on wheel event
body: <p>By default, <code>Flickable</code> scrolls on mouse wheel event: horizontally if Shift modifier is pressed, and vertically if no modifier is active. I'd like to override this behaviour to make it zoom in/out.</p>
  
  <p>I tried to use <code>MouseArea</code> as a child of <code>Flickable</code>. Defining desired behaviour inside <code>onWheel</code> handler I get what I want, but it breaks flicking feature. Motion of two touch points is recognised as a wheel event on my Mac, what prevents <code>Flickable</code> to steel this event (<code>MouseArea.preventSteeling</code> is <code>false</code> by default). So I get somewhat mixed zooming feature that respects velocity/acceleration behaviour of <code>Flickable</code>.</p>