Updated subclassing of credentials

[siuc-nate]

From @stuartasutton:
There were 2 (good) comments on the names of the organization classes. Here's my take after the only 2 comments. (ignore the placeholder for military...they didn't see that). They will be advised this AM that changes to the credential classification model is a separate conversation from their task on refining the definition of Certification (for people).

Originally posted by @stuartasutton in #544 (comment)

[siuc-nate]

Per our 9-3-2019 meeting:
This needs re-review.

The Mapping and Gap Analysis spreadsheet does contain a navy:requiresCredential property, but it does not point to any specific subclass of credential.

[siuc-nate]

Per our 10-13-2020 meeting:

Closing this - we can reopen later if needed.