Add QBoundedCircularBuffer and test

Change-Id: Ied0bd701fa653396b657ea5c2f2097eb7a425953
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
RenderNode using Handles

A RenderNode now holds a handle, a parent handle and handles to its children.
RenderNodesManager sets the handle of a RenderNode when a RenderNode is acquired.

Change-Id: I25f4fbb25b6a512dd815aa8671a2f85443365035
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>