Reduce liquid's whitespace for a few pages and move about menu to the end.

Also fix a couple of typos while at it and change header tags' order.

docs: New favicons and add a service worker

Include everything for most browsers to work including Android.

Kept favicon.ico to the root dir.

Also added a manifest.json for PWA.

Uses some if/else action to ensure there's readable text on hover. Swapped out a hex value to a variable while I was in there.

Fixes #23398, fixes #23351.

Fixes #23397

Just fixes small typo

* Remove remaining references to v4 Alpha

This commit removes the remaining refrences to the v4 Alpha website and replaces them with the
corresponding v4 Beta ones.

**Note:** We have to hard code the current docs version at some places. Wouldn't it be good to have a `/docs/latest/` redirect to solve this "issue" in the future?

* Don't update the domain in the CNAME file

There is no _custom.scss file anymore.

Gemfile was missing. Couldn't compile documentation when using npm.

Merge branch 'style-redirect-page' of https://github.com/JasonEtco/bootstrap into JasonEtco-style-redirect-page

Only applies the margins to .highlight instances within .bd-content, thus negating any need for #23279.

* use a mixin there
* revamp .btn-link to match default and outline variants
* remove unnecessary properties

move max-width: 100% on .container to the root of the make-container mixin so it's not repeated at compilation (#22947)

Update Jekyll to v3.5.2 and add `meta generator` tag

Bootstrap 4.0 Beta 1 dropped the offset classes in favor of using margin utilities. Update the blog example in the docs to use the appropriate `ml-auto` instead of `offset-sm-1` class to retain a pixel perfect with previous versions.