Closes #13379.

- Move example to correct location docs/examples/
- Move custom JS and CSS into stand-alone files
- Update headers and footers
- Copy-editing

Based on @pete-otaqui's work from #11851

Per https://github.com/paypal/bootstrap-accessibility-plugin/blob/d8fcbcd3fe86f0cb47fda0ffe269b2c7a2131f07/README.md#alert

The filename generated at dist/css/ called 'bootstrap-rtl.min.css'.

If you add an "active" class to one of the <li> elements in the top navigation, and style it so that active tabs have a different color, it becomes clear that there is a 1 pixel stray line under the navigation. This style fixes that.

Follow up to 1bdd59b18c2d1b2409d0422a60e8c007053202df, to better position the sidebar so the potential scrollbar doesn't get hidden by the navbar

Before: 1,12 MB (1.174.728 bytes)
After:  1,11 MB (1.173.614 bytes)