Better management of query type

[mboudet]

Since we now send queries on the protected endpoint, we should explicitly specify the query type.

Auto-detection fails in some case, because the lib detect the 'ASK' of askomic...

Basically SPARQLWrapper autodetect the query type based on content (ie: DELETE, ASK, etc..), and send 'modifying' queries on the protected endpoint.

Except that if we use prefixes in the query, the lib will always detect the type as 'ASK', and send it to the unprotected endpoint.

This 'works' most of the time, but fails when publishing a dataset.

Since we know direct queries (through the ASK interface, or the sparql query) can only be SELECT queries, we should not rely on autodetection, and directly force the query type. It will increase security, since for now users can delete graphs through the SPARQL console.