bump sesame and slf4j versions
remove aduna repository, as sesame-2.7 is going to be deployed to sonatype and maven central
add sonatype snapshot repository to fetch sesame-2.7-SNAPSHOT artifacts
remove aduna-commons packages that are not used independent of sesame
switch default N3 type from text/rdf+n3 to text/n3 per the current W3C Team Submission