Map view (#1520): entries of a diary that carry coordinates

Same keyset pagination as GET /entries, filtered to entries with a pin. A page can come back with fewer than limit items, or none, while hasNext is still true -- keep paging until hasNext is false to collect every pin. With withUnplaced=true the page also keeps entries that name a place but have no coordinates, with locationLat/locationLng null; without it both are always numbers.