Remove obsolete content from About page and move list of editors under acknowledgements

[mcking65]

Before launch, we need to simplify the about page to make it more useful to new-comers and remove content that is obsolete due to APG no longer being a TR document.

Needed changes to about.md:

• Remove dt/dd elements containing version links for this version, latest published, latest, editors draft
• Remove dt/dd elements containing links to TR history and Git Commit History
• Move editors and former editors to a subsection titled "Editors under acknowledgements
• Remove dd/dt elements containing feedback information
• Remove section with id=abstract
• Complete Move "Read me first" content from "About" page to its own page within fundamentals section #48 to remove the sections with headings of No ARIA is better than Bad ARIA, Browser, and Assistive Technology Support, and Mobile and Touch Support.
• Remove section for "Status of this Document" that starts on line 179

The result should be an about page with 4 sections with the following titles in H2 elements:

1. Introduction
2. Change History
3. Acknowledgements
4. References

This text file about.html.txt
contains HTML that represents the desired resulting structure.
Note that it is just the structure containing the current content, including movement of editors and former editors into an acknowledgements subsection. It is otherwise not the specific desired content. I am making edits to the introduction and change history in the main aria-practices.html file.

[mcking65]

Checked preview of #62 for all items in to-do list. All items are addressed by #62.

[mcking65]

Verified still fixed after today's changes to #62.