EPIC: Merge Module Usage project

Problem/Motivation

We have agreed to

Steps to reproduce

As a result of suggestions made in #3522587: Module documentation improvements we are planning to merge the Module Usage Documentation project into Content Model and Site Documentation project.

This will serve as the epic for that effort.

Proposed resolution

Initial idea is as follows, but needs more discussion and investigation. This is a work in progress.

- Move the Module Usage Documentation module in as a sub module
- Keep the enable, update, uninstall history
- Replace the "Notes" tab with a link to the CM Document if one exists, or to the Add form.
- Remove the links
- Create a migration that would migrate existing notes and links into an existing CM Document or create a new one if none existed. This migration should be triggered by four possible places. (hook_uninstall of Module Usage Documentation, hook_install of Content Model and Site Documentation, hook_update_n in both original Module Usage Documentation AND in the New submodule. I think it is needed in that many places to handle the various upgrade/install scenarios.

User interface changes

API changes

Data model changes

Remaining tasks

Make issues for the finalized plan