Doc: update the Android tutorial to also cover iOS

Rename as "Creating a Mobile Application".
Add the steps necessary for deploying to iOS devices.
Fix the link in the Tutorials tab in the Welcome mode.

Change-Id: Ie72bf087c789d8d1299b9b5ac19ad732da534012
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>