Improve FusekiExportService
Fix crashes when there are no commits in the datastore (e.g. developing) and when there are no public records the service - it now generates ttl correctly just for the catalogue itself.
Also cleanly replace existing triples if they exist to keep data in sync.
Also has some freemarker template edits to correctly add some prefix info.
Jira: EMC-47
Edited by Jonathan Cooper