Prevent the map stealing mouse events from the zoom slider.

Fixes using the slider to zoom the map.

Task-number: QTBUG-34237
Change-Id: I78b005030c3d869e63b9391e41d05ff28caa3cf5
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Add new markers at touched location.

New markers added in the mapviewer example were being placed at the top
left hand corner of the displayed map, just out of view. The user had
to pan the map to see the newly added marker.

Changed to position new markers at the location touched by the user to
activate the context menu.

Change-Id: If328e04cfd651a75fb91d599bedbd1129e761c7b
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>