Remove the ContainerResource from Datastream.  Monkeypatch RDF::DateTime
to support nanoseconds.
Merge pull request #501 from projecthydra/ldp_updated_fedora

Remove the ContainerResource from Datastream

This gets things working better with Fedora4, but still results in failures so it's being merged without regard to Travis. This commit also contradicts the previous commit 6eb6518 so some squashing might be needed.
Factors out behavior from ActiveFedora::Rdf::ObjectResource to mixin
ActiveFedora::Rdf::Persistence.

The change allows any ActiveTriples::Resource descendant which includes the mixin
to be used as the resource class for an ActiveFedora::RDFDatastream, rather than
requiring an ObjectResource subclass.

Conflicts:
	lib/active_fedora/rdf.rb
	lib/active_fedora/rdf/object_resource.rb
Update to ActiveTriples

This is as far as I’ve gotten trying to get the latest AT working with
Fedora4.  I cherry-picked from PR #500 as a start. The secret is to
apply the same changes in rdf_datastream.rb to fedora_attributes.rb.