add option for null OWLOntologyID in
PoddSesameManagerImpl.versionAndSchemaContexts

This feature was previously hardcoded into SearchOntologyResourceImpl to
get around the lack of the feature in PoddSesameManager
Start cleaning up the context definition mess by adding new methods to
public APIs
Remove duplicated method that is now unused
Remove another duplicated method that is now unused
Use Rio.write to simplify output
Fix NPE caused by Rio.write change
Merge branch 'redesign-search-ontology-labels'