show addtional marble themes

This is a simple change to show additional marble themes in a submenu below the map menu.

Many of the default themes are blacklisted as they seem not useful for the use in digikam. But if the user created additional themes they will be shown.

Here a screenshot of the change in action in the geolocation tool:

(edited) Here also a tar with the two swiss topo webmaps based themes. To be extracted directly in the users home dir: swiss_topo_marble_themes.tar