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)

- Also fixes the vertical alignment of labels in horizontal layouts on
account of the recent button and input padding changes
- Also changes the vertical alignment of the checkboxes and radios in
horizontal forms

* Moves input groups CSS into separate file
* Moves input groups docs into the Components page
* Add support for radios and checkboxes in input groups to fix #8679

* Fix alllll the links!
* Change all `*.js` in JS plugin docs (no mo `bootstrap-`)
* Fully remove `tr.info`
* Bring nav includes up to date

* Update example sections to include basic, mobile-desktop, and mobile-tablet-desktop implementations
* Add more examples to the grid example page
* Red columns instead of gray for more Bootstrapy aesthetic

* Bring back the navbar up top
* Pull the docs content back into separate pages because a 6.6k line docs file is just crazy
* Recenter the page content and bring back affixed side nav (needs work)