Refactor queries for fetching&counting the geometries

[hannahbast]

There are now three predefined queries for fetching the geometries from a SPARQL endpoint: one using geo:asWKT (the default), one using wdt:P525 (used for backends where the name starts with wikidata), and one using a SERVICE request to Wikidata (used for backends where the name starts with dblp). Apart from these differences, the queries have the exact same structure. The query for counting the number of geometries is now automatically derived from the fetching query, in a way that is as efficient as possible (in particular, more efficient than before).

[patrickbr]

Thank you, @hannahbast, this looks good!

However, I don't think it is a good idea to set QUERY_ASGEOMETRY as the default return value in getQuery() (also, I think it should be named QUERY_HASGEOMETRY). AFAIK, this query is only relevant for historic osm2rdf outputs in which objects are linked directly to their WKT string via geo:hasGeometry. This is not following the GeoSPARQL standard. IMHO the default should be QUERY_ASWKT, as this follows the standard.

This default fallback is already present in the current master and (as I just realized) is the reason I couldn't use master against OHM this afternoon during our meeting: in the old master, OHM wasn't handled explicitly, and the fallback query (equivalent to the query now called QUERY_ASGEOMETRY) then returned the intermediate geometry objects, not the WKT strings. Essentially, RDF data that follows the GeoSPARQL standard but is not explicitly handled in getQuery() is currently unusable with master, and also still with this PR.

We should drop QUERY_ASGEOMETRY completely, make QUERY_ASWKT the default in getQuery() and also remove the explicit handling of OSM and OHM in getQuery().