Docs cleanup

Add Wall of Browser Bugs entry for IE bug from issue #14211

Document limitations of buttons JS plugin

Use autocomplete="off" in buttons plugin docs examples

[skip sauce]

Charlesbjohnson affix bottom when dynamic height

Mckramer dropdown aria

Conflicts:
	docs/_includes/js/dropdowns.html

Update grunt-csscomb

Document that form field feedback icons only work with input.form-control

Closes #14202.

[skip sauce]

Use HTTPS in CDN URLs in _config.yml

Fix popover dismiss-on-next-click example

For consistency with the rest of the docs and per our code guidelines.

[skip sauce]

Not clear from the spec whether this is invalid per se.
But it is the current best known workaround for Firefox's unusual behavior.

Refs #13875.

Addresses #14148.

  document height is smaller than the viewport height.

  in order to handle multiple edge cases, specifically when the document
  height is dynamic.
Always reposition an affix that is affixed to the bottom.

speed up js tests a bit

Tabs to spaces in variables.less

Follow-up to #13907: simplify JS logic for focus shim