Small content corrections

[wendellpiez]

User Story:

Two content corrections are required to catalogs and profiles (see #385):

Rev 4 Catalog

In the rev 4 catalog, where it has (line 1235)

<rlink href="NIST_SP-800-53_rev4_catalog.xml" media-type="application/oscal.metaschema+xml"/>

The media type should be application/oscal.catalog+xml.

Anywhere publication-date is used

Switch the value to a string conformant to an ISO 8601 date-time including Time Zone.

Document this usage in the schema docs until Schematron can be applied to validate it and/or Metaschema can be extended to support xsd:dateTime.

For this element (and check on any/all date elements) the requirement should be a valid ISO 8601 value with time zone expressed.

Goals:

Correct errors or lapses as described above.

Dependencies:

In connection with PR #385, make these changes in the branch wendellpiez:issue166-ref-refactoring, permitting it to be merged.

Then, rebase the later branch issue172-renaming-class-flag over the merged branch.

Acceptance Criteria

1. We have consensus on handling dates
2. We have made the changes noted above, and a PR is produced to merge these changes in.

[david-waltermire]

This is complete.