first pass at creating rdf graph with provenance

we have code that produces a graph that doesn't fail.
new conjunctive graph is queryable

muscle() upgraded to work with new conjunctive graph
first rough implementation of get reference
adding method to write db out to sql dump
first stub description of add_reference
make get_reference return None if missing ref
Clean up to make get_references more real

Still only have reference data (fake) for one receptor.