Implement support for gx:TourControl and its base classes. Add a GeoDataTourPrimitive (abstract) class and a GeoDataTourControl which inherits GeoDataTourPrimitive.

Add a gx:Playlist tag handler and a GeoDataPlaylist class. The playlist should accept an arbitray number of GeoDataTourPrimitive children (similar to GeoDataContainer) that can be added and removed.

Extend the existing TourTest.cpp (see https://git.reviewboard.kde.org/r/108349/ ) by a Playlist with some TourControl children.