Geomaps: adapt to Core changes pt.4 (#699).

Geomaps are functional again.

BREAKING CHANGE

Geomaps API:

The topic returned by the `getDomainTopic()` service call does *not* include its child topics.
When you need the child topics:
    - Java API:
        - on-demand loading (selectively): just call the accessors of the topic's composite value, e.g. `topic.getCompositeValue().getString(...)`. The respective child topics are loaded on-demand.
        - explicit loading:
            - `topic.loadChildTopics()` loads all child topics
            - `topic.loadChildTopics(childTypeUri)` loads child topics selectively
    - REST API: add `fetch_composite=true` to the query parameters. All child topics are included in the response.

See #699.