Improvements to metaschema, schemas and samples

[wendellpiez]

See Issue #327.

Committer Notes

Includes incremental changes to metaschema design including better support for modular metaschemas and new modules for metadata and resources, shared by catalog and profile schemas. Many improvements to metaschema design for usability (thanks @brianrufgsa ).

Experimental metaschemas for the implementation layer are left in place; they may require adjustment.

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you squashed any non-relevant commits and commit messages? [instructions] This is a single commit

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them? More documentation on Metaschema in general is called for
• Have you written new tests for your core changes, as applicable?
• Have you included examples of how to use your new feature(s)?

[anweiss]

LGTM. Only contains metaschema-related changes which is exactly what this PR describes.

[david-waltermire]

This looks good.