Support new properties

[PR0CK0]

First off, @nicholascar, love your project. It's amazing for demoing ontologies to clients. Anyhow, there are a few commonly-used properties that are not supported and would be nice to see for more metadata. Not sure if I can just edit the properties .py file myself and have it work, because I'm using CLI. If I can do that, let me know and I'd be happy to merge request.

Annotation Properties:
skos:prefLabel
skos:altLabel
skos:editorialNote
rdfs:seeAlso (#174)

I use these a lot when describing the ontology itself:
dct:subject
dct:audience
dct:format
dct:language

Other:
owl:equivalentProperty (#175)