investigate new GraphQL wikidata endpoint

[nylki]

Currently several network requests get data from the wikidata query endpoint. Now there is a new GraphQL API that is supposedly more efficient: https://www.wikidata.org/wiki/Wikidata:Wikibase_GraphQL

Potentially current queries could be refactored and performed by this new API if it delivers the data we want. The amount of returned items is important too, the currently used SPARQL endpoint can return many hundred or thousand items per request (whereas the action API is more limited).