Adding geosearch/geocode of Vlaanderen

[tobieumans]

https://geo.api.vlaanderen.be/geolocation/

[finnp-sogelink]

Add Nominatim Geosearch

• Update geocoder URLs
• Update response parsing
• Find CORS workaround
• Make function generalizable: be able to switch between PDOK and OSM Geosearch

[finnp-sogelink]

Ready @kamielverhelst