Add geocoding lookup list to configuration

[JeroenDeDauw]

Something like

$egMapsHardcodedGeocoding = [
    'Berlin' => '52.517037 N, 13.38886 E',
    'London' => '51.507322 N, 0.127647 W'
];

If the value being geocoded is found in this list, the corresponding coordinates would be used rather than the real geocoding service.

This allows fixing incorrect coordinates for a specific usecase or to have limited "offline support" for important locations.