Feature/persist datastream to triple store

DO NOT MERGE THIS

I just want to talk about it. This uses the triple-store as the read mechanism for datastreams, because new relic says getting descMetadata's content out takes ages. It works, but merging requires two things:

A) We would have to make blank nodes work for RDF::Resource. Right now you wouldn't be able to get it back out - needs a test.

B) We'd have to run a rake task right after merging the first time to populate the triplestore with what's currently in datastream_content.