Revise Geomaps API wording (#645).

The `Geomap` model class is now an iterable over its Geo Coordinates.

BREAKING CHANGES in Geomaps API:

Renamed:
    getGeoTopic(long topicId)                     -> getDomainTopic(long geoCoordId)
    addTopicToGeomap(long geomapId, long topicId) -> addCoordinateToGeomap(long geomapId, long geoCoordId)

Dropped:
    getGeomapTopics(long geomapId)

RESTClient:
    dm4c.restc.get_geotopic(topic_id)                   -> ..get_domain_topic(geo_coord_id)
    dm4c.restc.add_topic_to_geomap(geomap_id, topic_id) -> ..add_coordinate_to_geomap(geomap_id, geo_coord_id)

See #645.