Add support for linking to Yasgui from SPARQL-Endpoint distributions

[jakubklimek]

For the C3V9 deliverable, we need to add link to Yasgui for distributions of the SPARQL endpoint type. The Yasgui location needs to be parametrized in case we need to deploy it on our servers.

• Example dataset
• Default query:

  SELECT ?typ (COUNT(?s) AS ?pocet)
  WHERE {
  ?s a ?typ
  }
  GROUP BY ?typ
  ORDER BY DESC(COUNT(?s))
  LIMIT 10

Conditions of showing YasGUI link:

• Specification is https://www.w3.org/TR/sparql11-protocol/
• Endpoint url is specified, i.e. https://data.mvcr.gov.cz/sparql in the example