SES-1866 : Add XMLWriterSettings

Initial setting is to allow users not to print the XML PI, for cases
where the stream already has the XML PI and possibly other information
already printed to it
SES-1866 : Use INCLUDE_XML_PI setting in RDFXMLWriter
SES-1866 : Add INCLUDE_ROOT_RDF_TAG setting

The rdf:RDF root tag is optional, although recommended. This setting
tells the RDF/XML Writer not to print it if the user has already printed
it or does not need it to be automatically printed.
SES-1866 : Support INCLUDE_XML_PI in SPARQLXMLWriter
SES-1866 : Fix for INCLUDE_ROOT_RDF_TAG to ignore entire tag printing
SES-1866 : Support INCLUDE_XML_PI for TriX writer
SES-1866 : Fix to use xmlns=... if root rdf tag is not written
Merged in ansell/sesame/SES-1866 (pull request #158)

SES-1866 : Add XMLWriterSettings
Merge branch '2.7.x'