Add functionality to expand/collapse sections of the checklist, or the entire checklist page

Each section of the Checklist (Content, Keyboard, Controls, etc.) should have the ability to mass-toggle each details element in it open or closed. Additionally, it would be great to have a toggle that could do this for the entire Checklist page.

The global toggle should override expanded/collapsed state for each section, as it is the "parent" control. The toggle should be accessible, and the underlying JavaScript should be ES5, to ensure good support for legacy browsers.