First working version (#633).

New API for performing a proximity search.

Geospatial API:
{{{
import de.deepamehta.plugins.geomaps.model.GeoCoordinate;

List<Topic> getTopicsWithinDistance(GeoCoordinate geoCoord, double maxDistanceInKm)
}}}

REST API:
{{{
GET /geospatial/<lon>,<lat>/distance/<km>
}}}

Returned are Geo Coordinate topics (as defined in the Geomaps module).

Each time a Geo Coordinate topic is created or updated its values are automatically indexed by means of Neo4j Spatial (http://www.neo4j.org/develop/spatial). That is typically each time an Address topic is created/updated, e.g. when editing a Person or an Institution.

Existing Geo Coordinate topics are not yet indexed (this remains to be implemented). Only create and update operations are respected at the moment.

There is a bug in Neo4j Spatial: when the above API is used while the geospatial index has no entries yet, a NullPointerException is thrown.

Hint: with a Geo Coordinate topic at hand you can retrieve the corresponding domain topic (e.g. a Person or Institution) by calling the Geomaps service's
    `Topic getDomainTopic(long geoCoordId)`

See #633.