Doc: change filename and page name to match title

The Android app tutorial is now a more generic mobile app tutorial, so
it was moved to qtquick folder and renamed as creator-mobile-app-tutorial.qdoc.
The page name (HTML) was also changed accordingly.

Change-Id: I749f45a611b32204e5551884238f79d3d3b639fa
Reviewed-by: Sergio Ahumada <sahumada@blackberry.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>