Speed up the test a bit..

Using hundreds of thousands of Items works, but it takes its
toll, so use a custom item to allocate QSGNodes directly which
are instantanous.

Change-Id: Iee5d8495b3d7d5abd24c14a53b2327e5efe9523b
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Clean up Image and ShaderEffectSource properly.

Change-Id: I9e3eb5f65ea5f46d30fb7905d0f9c479da367bf5
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>