Implement functionality for manually adding a tileJSON URL including checks for required attributes

[codehub-rony]

It is possible that the required TileJSON for creating a OGC vectortile layer #4 could not be found. In that case the user:

• should be notified/informed about the issue
• should be able to add the TileJSON URL manually

After parsing the TileJSON, a basic check should check if the geometry_type is defined. If not, the geometry_type should be manually added.