Reasons for creating this PR

Wikidata URIs were not being resolved properly, see #1911. This PR works around the issue by switching to the alternative QLever Wikidata SPARQL endpoint which is much faster and (hopefully) more reliable than the Blazegraph-based official WDQS.

Link to relevant issue(s), if any

• Closes Wikidata mapping queries are not working #1911

Description of the changes in this PR

• switch to QLever SPARQL endpoint for resolving Wikidata entities
• rename some classes (WDQS -> Wikidata) to avoid confusion, as we are no longer using WDQS

Known problems or uncertainties in this PR

I hope it really helped solve the problem?

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)