Add option to fetch geometries via geo:hasGeometry/geo:asWKT (#10)

* Update the geometry predicate for OSM

So far, the code supported getting the geometries via `geo:hasGeometry`
(old osm2rdf style) and via `wdt:P625` (Wikidata style). Since November,
the TTLs provided on https:/osm2rdf.cs.uni-freiburg.de provide the
geometries via geo:hasGeometry/geo:asWKT, which is now also supported.

TODO: The selection between is currently hard-coded, based on the name
of the backend. We should find a more elegant and robust mechanism for
this.

* make duplicate report a DEBUG message, output cumulative number of duplicates, update util lib, don't output WKT bbox in log if box is empty (ugly)

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Co-authored-by: Hannah Bast <[email protected]>
Co-authored-by: Patrick Brosi <[email protected]>