Added the removal of tab-content and tab-pane in the migration guide

Fixed some errors in the documentation

Added link to Ukrainian translation website (in about.html)

Remove redundant, duplicate comment

Fixes #11610: Add @grid-float-breakpoint-max to better link navbar behavior across viewports and improve customization.

Also addresses #10371, #10395, and #10465.

Update 3rd party asset libraries

Conflicts:
	dist/css/bootstrap.min.css
	docs-assets/js/raw-files.js

Fixes #11436: mention in docs that .container isn't nestable; update docs to mention width, not max-width

Updates Jumbotron thumbnail

Dropping unused variable in dropdown.js

Dropping an unused variable in the Dropdown function inside the `dropdown.js` code.

There are no new/changed unit tests, as there are no feature/bug changes requiring new test cases.

For the record: I agree to dual-license this contribution under the Apache 2 and MIT licenses.

Add a migration tip for .label to .label-default

Conflicts:
	dist/css/bootstrap.min.css

fix .btn-group-xs portion of #10979

switch to Sauce Labs for our cross-browser JS unit testing needs

Fixes #11087

type="button" doesn't make sense for an <a>

http://caniuse.com/#search=grad

document that XS grid supports offsets and push/pull