Pull label from RDF stream for serialization formats

- Add getSerializationTitle to bridge HAS_SERIALIZATION -> IS_IN_FORMAT -> RDFS_LABEL gap
- Add to dc:format to Repository objects to cover mode:root nodeTypes (homepage of admin interface)
- Remove hack from getObjectTitle
- Modify common-node-actions to use new serialization Titles for both export and import select boxes

Resolves https://www.pivotaltracker.com/story/show/65221404