Refactor IRI class

[bivens-dev]

Right now the IRI class has multiple roles which should be split out.

The concept of an IRI should be a stand alone one that is entirely detached from the concept of being a RDF node in a graph.

Also once the work in #6 is completed we should look to use that to get closer toward actually implementing RFC 3987 specification and use a URI as the underlying data structure now that we should be able to safely store IRIs as valid URIs.