Doc: Adding "QML Application Developer Resources" guide.

-ported from qtdeclarative.git
-fixed snippet and image paths to doc/snippets and doc/images

Because this guide will need to cover more than Qt QML and Qt Quick,
this guide does not need to be in qtdeclarative.

Change-Id: Id6a47420a1e73b5c55b7233571557e3558e82043
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>
Reviewed-by: Geir Vattekar <geir.vattekar@digia.com>