Some map services offer their maps only for a limited region, so we need to show those links when the user is viewing only that region.
* We could add geojson (geometry) field to the config file to specify the relevant region
* The client could either see them based on the map view center, or overlaping bounding box
* The geojson data will be stored in a separate file on the server, and merged with the externalData to minimize the payload (only referenced geojson objects will be attached to the result)
Schema:
```lang=json
{
"regions": {
// Value as returned from geoshapes service, GeoJSON's "geometries" field
"US"Q30": {"type":"GeometryCollection","geometries":[{"type":"Polygon","coordinates":[[[-176.686, ...},
...
}
"services": [
{
"id": "us-and-canada-service",
"featured": true,
"region": ["US"Q30", "Q16"], // US, "CA"],Canada
...
```