Implement support for the NetworkLink KML element and some (not yet all) of its sub elements:

• Add a NetworkLink class which inherits GeoDataFeature and has getters/setters for identifier, refreshVisibility and flyToView
• Add a kml handler for NetworkLink. Have it extract the identifier attribute. Handle the parent element in the same way as KmlPlacemarkTagHandler.cpp does (i.e. append itself to parents that are containers)
• Add kml handlers for refreshVisibility and flyToView. Have them check their parent to be NetworkLink and set its values accordingly
• Add a TestNetworkLink.cpp test to the test suite. Have it test parsing similar to TestScreenOverlay.cpp

References:

• https://developers.google.com/kml/documentation/kmlreference#networklink
• http://marble.kde.org/kml-guide.php