Refactor WissKI SPARQL endpoint

Problem/Motivation

We have a nice HTML SPARQL console at /wisski/endpoint/. At this point its only a console for queries response with html tables. We have the possibility to send a "query" parameter, but no option for response format like json, xml or csv. We may want to implement:

1. Securities checks and restrictions (permissions etc.)
2. Query escaping (character encoding etc.)
3. Response formats
4. More sophisticated query options