Draft: Added the possibility to display theme favorite icons in the menubar

Added the possibility to display theme favorite icons in the menubar.

To make use of it, add favorite to the theme in themes.json.

f.e.

...
    "themes": [
        {
            "id": 174,
            "name": "Amtliche Vermessung",
            "icon": "https://map.geo.bs.ch/static/ec784733b62749f4a6ba20011cbea803/images/themes/AmtlicheVermessung.png",
            "location": [2779500, 1179500],
            "zoom": 6,
            "favorite": true,
            "children": [...]
            ...
       }