Naming convention of StixRegion and URI

[brett-heffelfinger]

Related to #44, #86

When implementing the STIX Region vocabulary, I had made the URI gist:StixRegion with a skos:prefLabel of "Region" as that's what STIX calls the category of individuals on the site. I did this to differentiate a StixRegion from other URIs like if we had something like gist:Region somewhere else that would clash with the category URI.

Decisions to be made:

• Is the URI for gist:StixRegion correct or should it be changed?
• What should the appropriate skos:prefLabel be? (Note: I assume it should match with whatever URI we decide on, but we may need or want to have a number of skos:altLabels to cover readability.)
• Unrelated somewhat, but should we add gist:stixTerm to the categories themselves to cover STIX tags like region-ov for this subset?