Fix handling of btn-group placed inside input-group-btn (used for mixing dropdowns with normal buttons)

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.

revert an earlier change to move the component-animations.less file because it fubared modal backdrop .fade usage

Fixes #11770: Move component-animations.less to the utility section of import list to match Customizer

Fixes #11588: Scope font-size to only p elements in a .jumbotron and remove the supersized line-height from the base class

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

Fixes #11561: Add float: left; to .form-control within input groups to prevent IE9 from screwing up placeholder text and select menu arrows

* Floats any `.input-group` within a toolbar
* Simplifies the CSS to remove sibling selectors and instead use a
negative amrgin on the parent with only `margin-left`

See it in action: http://jsbin.com/aGEcUqAT/1/.

* Removes an old pair of selectors that didn’t properly target the
right-aligned navbar alignment of dropdown menus.
* Deprecates the `.pull-right` alignment in favor of a more specific
and unique class name.
* Adds `.dropdown-menu-right` as the new alignment class. This is then
mixin-ed into the `.navbar-right.navbar-nav` dropdown menus for
auto-alignment.
* To override that auto-alignment, use `.dropdown-menu-left` as needed.

Fixes #10495: Float Glyphicon and set margins in .navbar-brand to ensure there is no added height because wtf even is CSS

Original discussion:
https://github.com/less/less.js/issues/1437#issuecomment-21383639.

Since we’re switching to `grunt-contrib-less`, we can take advantage of
newer LESS features than what RECESS supported. Included in that is the
ability to `:extend`, and not only that, but `:extend(.mixin-name
all)`. By doing so, we remove duplicate CSS for all our elements that
were being clearfix-ed.

Fixes #8947, #8968, #8991, #9257, #9268, #9291, #9430, #9604, #9686,
#9929, #10731, #10793, #11305, #11498, #11533, #11570, #11604, #11652.

(dem issues, tho)

add vertical-align back to where it's necessary since we reset from block to inline-block on several inputs

/cc #10711 #9862

* Adds nav link to sidebar for contextual classes
* Refactors to use prefixed classes, like .list-group-item-info, instead of chained classes
* Adds default and linked variations to example in docs

Fixes #11766: Use color var for background on badges in buttons to restore proper background to default button badge

reverted changes in commit 96109d31 which seemed to break conditional classes in striped tables (ignoring the comment above that the previous rules were needed for just this purpose)

fixes issue #11728