Doc: Re-organized Qt Quick's examples page.

-Organized into "Demo", "Tutorials", and "Examples".
-Added Controls, Dialogs, and other Qt Quick examples.
-Added links to Qt Creator tutorials related to Qt Quick.

Task-number: QTBUG-36838
Change-Id: I9ca000a73465217a2c42ebac9288e6462afa4cf5
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>