Linking to datastream fcr:metadata in HTML UI

Fixes https://www.pivotaltracker.com/story/show/80952408
That was my point about entailment. But we should make this explicit. Even with that proviso, we are going ahead with a design that says, "You will get different RDF when you retrieve this URI depending on your conneg." which is... weird. That's why I want to make the point about entailment explicit. And it still feels, frankly, like a dangerous idea. I guess I still don't understand why we want the "extra" triples in the HTML anyway.