Add rollerball example to show rendering and physics basics

At present it only exercises the renderer but it will be extended
to also cover the physics aspect too.

Change-Id: I83217f09eeb3471b8a508fa8a8948410ad1e1d58
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>
Expose window to qml to set aspect ratio of camera

This doesn't work yet as the CameraLens component doesn't yet notify
observers of changes. This will come in the next commit

Change-Id: I4b3d5c955c514711c79788a9b3f27f71884d2c97
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>
Notify observers of changes to the camera projection matrix

This now allows the camera in rollerball example to track the window's
aspect ratio - resize the window a little to kick it into life until
the patch gets merged that queues up notifications until an observer
becomes available.

Change-Id: I22c41f6f576b85a89d14aa7732d2f2b1cdc3fa2b
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>