Added qml function to fit map to geo shape

Added a qml invokable function in the map object to fit the viewport
to a geo shape. It's heavily influenced from fitViewportToMapItems.
Also added some basic ui tests.

Added handlig for the case with an empty shape

Change-Id: Iecad849f2c1b6d9a54eab90e26435b31a138886c
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>