Cleanup and fix the Getting Started tutorial

The tutorial got messed up by 04cb8ef1. This change restores the core/
folder from within the gsQml/ backup folder and then deletes it.

Task-number: QTBUG-31082
Change-Id: Ie18af90dbc70812dc7e74fdd1389a8734cf62fd4
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>