Fixes #13583: Move .sr-only and .sr-only-focusable to mixins, then use them to create classes in _utilities.scss

Conflicts:
	.gitignore
	Gruntfile.js
	_config.yml
	dist/css/bootstrap-theme.css
	dist/css/bootstrap-theme.min.css
	dist/css/bootstrap.css
	dist/css/bootstrap.css.map
	dist/css/bootstrap.min.css
	dist/js/bootstrap.js
	dist/js/bootstrap.min.js
	docs/_includes/components/navbar.html
	docs/_includes/components/progress-bars.html
	docs/_includes/css/grid.html
	docs/_includes/css/overview.html
	docs/_includes/customizer-variables.html
	docs/_includes/getting-started/accessibility.html
	docs/_includes/getting-started/browser-device-support.html
	docs/_includes/getting-started/community.html
	docs/_includes/getting-started/disabling-responsiveness.html
	docs/_includes/getting-started/download.html
	docs/_includes/getting-started/examples.html
	docs/_includes/getting-started/license.html
	docs/_includes/getting-started/third-party-support.html
	docs/_includes/js/alerts.html
	docs/_includes/js/buttons.html
	docs/_includes/js/carousel.html
	docs/_includes/js/collapse.html
	docs/_include...

Input group sizes: Properly position `.form-control-feedback`

Fixes #15074

Update .visible* classes to use !important on table elements

Conflicts:
	dist/css/bootstrap.css.map
	dist/css/bootstrap.min.css

Darker style focus/hover on active buttons

There is no jshint:src task

Remove wrong role="tabpanel" from docs

As per discussion on https://github.com/w3c/wai-wcag-quickref/issues/2
and #13554

Make .bg-variant adjust :focus color in addition to :hover color

JSCS: Add "disallowSpacesInFunctionDeclaration"

Valid:

    function a() {}

Invalid:

    function a () {}

Jumbotron: Putting heading font size in variables to allow for easier overrides

Closes #16047 by merging a tweaked version of it.

Only disable pointer-events on disabled <a> btns

remove redundant aria-hidden usage from Modals

Document how to disable transitions in jQuery plugins

Properly document $(...).tab('show') method