Context: print info if txs are used or not
Context: switch to Logger based debugging for remaining query related messages
Context: remove dead code
Context: tighten interface by making only internally used methods private
Context: add support for general remote SPARQL service and 4Store triplestore

This patch enhances triplestore support to support remote SPARQL service.
It also adds support for 4Store triplestore which does not provide proper
Jena Model API hence remote SPARQL service support is used in this case.
Merge branch 'remote-sparql'