SES-1803 : Refactor NTriplesUtil.append(Literal...

Now uses the new isLanguageLiteral and Literals.hasNonNativeDatatype
methods to determine whether to write out language tags or datatype URIs
SES-1803 : Reuse NTriplesUtil in SPARQLFederatedService
SES-1803 : Reuse NTriplesUtil in QueryStringUtil
SES-1803 : Add escapes for \b and \f to NTriplesUtil.escapeString