Per #20513 a11y - improve sidebar document outline

Addressing Joe Dolson a11y review on ticket 20513: Headings: "It's a little confusing, with the sidebar appearing as a subheading under article titles in the headings hierarchy, but it meets the requirements."
Per #20513 a11y - switch underlines :hover :focus

Addressing Joe's a11y feedback: "The switch between the default view of links and the hover/focus view is slight; it would be very helpful you if added a change to that alternation that didn't depend on color. For :focus, you've got the outline, but for :hover, it's just a subtle color change. Removing underlines on :hover and :focus can be very effective." Removed default underlines and added them for h1 header.
Per #20513 a11y - add Aria nav role to footer
Version 1.8.3