Use RDF equality when diff'ing user-provided triples against stored triples
Merge pull request #552 from fcrepo4/jena-graph-containment

Use Jena's notion of graph containment instead of our strict equality
Implement a Converter<Resource,FedoraResource> to replace the Node converter
Use FedoraResource#getContainer/getChildren when serializating resources

Also, update getContainer + getChildren to be pairtree aware.
Move dc:describable into the fedora namespace
Add support for ServerManaged preference
Apply server-managed preferences to getResourceTriples()
Stop using PropertiesRdfContext(javax.jcr.Node) constructor
Split out discrete RDF Contexts from PropertiesRdfContext
Mark MODE, MIX, JCR_NT, and LDP as managed namespaces
Allow clients to send Prefer header to control what properties they intend to operate against

This allows clients who only have a partial representation of a resource to use
PUT operations to replace only the triples they are aware of, or provide hints
to the server about what triples they intend to operate on (for e.g. PATCH)

e.g.:

PUT /a
Prefer: handling=lenient;
omit="http://fedora.info/definitions/v4/repository#ServerManaged"

... only non-managed server properties ...

or

PUT /a
Prefer: handling=lenient; received="minimal"

... only the minimal representation ...