Add link shortener to share queries

[nichtich]

Requires a persistent database of queries and short links.

[nichtich]

Better use an existing link shortener like https://academiccloud.de/de/services/urlshortener/

Requires to configure a shortener with its API in the app and a way to return shortened URLs from queries (either additional method e.g. /api/sparql/link or as part of the HTTP Header in SPARQL response).