Feature/omit xs from grid

Update visual tests.

Change .tag print styles to .badge.

Fix padding on .bg-faded demo.

it's → its

Small grammar fix.

Fix MS A11y UserVoice entry in Most Wanted Features list

And move one Firefox entry to keep the entries sorted by browser.
Refs #21089

Refs #21089
[ci skip]

Linked to slack

Fix broken and redirected links.

Scope ::first-letter selector for print styles

`*::first-letter` causes problems in IE11 - only prints first page of a
multi-page document

Add Safari skip link bug and Firefox/Edge AT focus feature requests

These would help in making hidden skip links show up visually once they
receive AT focus (for sighted/partially sighted AT users)

The new breakpiont-limited class pattern is to omit the breakpoint size when using the lowest size eg. col-xs-12 to col-12. This commit implements this pattern to the grid system.

* Explore responsive display utils, but with a twist: lowest breakpoint has no breakpoint modifier in the class name
* make floats use the same format, add float-none mixin

* make spacer utils responsive by grid tier
* update scale to add two levels, document them
* change responsive spacing utils to avoid the xs abbreviation in the class name for that tier
* update code snippet to match source
* update usage in our docs
* linter
* docs updates

* Fix #17964

Some browsers are lazy when updating dom elements after transition effects. This can be fixed by reading element properties such as offsetHeight or offsetWidth. However, creating a function using the Function constructor just to access such element, results in a violation of Content Security Policy (where applied), which in turn crashes the application. This fix actually reverts to the way this was handled in v3 and should work as intended.

Firefox requires a width and flex-basis value to size the input field correctly. Despite the width being 1%, the input will size correctly at all parent widths.

http://codepen.io/zalog/pen/bpMJmv

floated content has to come first in the DOM, otherwise you can get alignment bugs. in flexbox though, that's not the case. as such, i'm adding this example code to guide folks to the changes needed to move between default and flex modes.