Define updated model document and templates for OASIS specifications

This work has two major parts:

• Define model OASIS specification in HTML for approval.
• After approval, upgrade templates and processes so that the HTML output (at least) will follow the approved model.

This will affect multiple templates in DOCX, ODT, Markdown, and likely other formats, and will require coordination with TCs using DocBook, DITA, ReSpec, XML, and other document preparation systems.

This will also affect the "Notes" model document and templates.