Persist OriginalRecord

This is a substantial rewrite of OriginalRecord to allow them to persist to LDP.

This isn't mergeable until the forthcoming Marmotta `3.3.0` release and a corresponding update to `marmottawrapper`.  Until then, I submit it for sanity check.
cbeer/ldp didn't quite work in the marmotta context and @cbeer indicated that we shouldn't pursue it, anyway.  I think this is heavier than he thinks we should have, and ends up having a lot in common with his Resource, but is maybe a better starting place for pursuing an `ActiveTriples::LDP`. In the meanwhile, it actually runs against Marmotta.

My biggest hesitation is the dependency on `#rdf_subject`, which already looks odd when posting LDP-NR's to Marmotta.