Fix qmake -r by moving load(qt_parts) to the end of the project

This is an issue for non-developer builds of Qt where the forwarding
headers have to be generated before processing the examples project
files.

Change-Id: I683227c97a763c48b8ab090580f37f7134680c59
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>