Split off from T211474 as a first step
By default the query service uses Wikidata's logo and favicon (with a looking glass overlay). As more installations of it pop up they still use the Wikidata logo and favicon while they really shouldn't.
- The logo can be configured more easily than before
- The favicon can be configured more easily than before
- The configuration works in the same way as other UI configuration does.
- the same actual logos should be used for now.