Doc: Adding platform extras example pages into the main examples page.

-better visibility to those examples.
-also added Active Qt link.

Change-Id: I3f4aa3e967bd3618f8739dfcdd5b4ba1ea5ee4e5
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>