Closes #14951 by merging it.

Transform text in components with text capitalization classes.

Moving the embed to it's own CSS file, moving the docs to the Components page with an example, fixing a Glyhpicons list problem in the docs

Don't copy-pasta all the Sass docs because fuck keeping that up to date. Instead, point to https://github.com/twbs/bootstrap-sass/blob/master/README.md.

New stuff:

* Adds `.has-feedback` and `.form-control-feedback` to show icon-based
form feedback to users. Fixes #11836.
* Removes the `width: 1em` on `.glyphicon` because it makes it
impractical to resize the width of all icons, even if they’re not
“empty” (e.g., a simple `.glyphicon { width: 30px; }` wouldn’t work,
nor would a class preceeded by a parent class.

Clean up:

* Sets `width: auto;` on all `.form-control`s within inline forms.
* Removes all the inline `select` menu `width` styles because all
inputs are now `auto`.
* Update form states docs to separate out sections better.

Fixes #11572: Add contextual background-color classes to match text classes; move both sets of classes to Helper Classes section of the CSS docs

/cc #10711 #9862

finish up second pass through docs nav, headings, organization, naming, etc (another run through at #9710)