Fix massive "bug" in _execSparqlUpdate, remove _execSql and extend addStatement

Fix: addStatement only adds new triple to the Store if there
is an sparqlQuery call afterwards or some function which
uses odbc_result. If not, no triple will add to the backend.
Problem was _execSparqlUpdate, which has now a simple
odbc_result call to "fix" that, ugly but its seems to be
working.

Extend addStatement to use string objects instead of array. If you
choose this way, than you will lost datatype and language settings,
but addStatement checks if URI or Literal too.