Create initial Dublin Core indexer framework and REST API endpoint.

/objects/PID/oai_dc will return an OAI Dublin Core document, and
(as-configured) willfirst try to get it from a Well-Known path (e.g.
"DC" datastream), or by looking at dc:* properties of the object.
Merge pull request #29 from futures/DublinCoreIndexer

Create initial Dublin Core indexer framework and REST API endpoint.