Add a PinchArea element

MouseArea and Flickable provide a declarative API for handling touch input. The most common touch interaction that is not handled is pinching (zoom, rotate, two finger drag). PinchArea handles this use case, providing a high-level declarative API (similar to MouseArea drag), and an imperative API for more specialized use. PinchArea must interact well with existing elements that handle touch: MouseArea, Flickable and PathView. The PinchArea implementation must handle the two primary use cases:

• zooming content in a Flickable
• allowing an item to be scaled and/or rotated and/or dragged.