Update scrollspy.js

Scrollspy target in tab content does not work properly. Calling .parents('.active') will return all parents with an active class (including the tab pane). Changing this line to .parentsUntil(this.options.target, '.active') should resolve the issue. This will scope the query to only search for active elements inside the scrollspy target.
Added unit test for removing only active class from within the scroll spy key.
Fix: IE10 or lower incorrectly determines the scrollheight of the body. Use document.documentElement for IE. To make this browser agnostic, the maximum scrollheight of both body and documentElement is used.
Fix: IE10 or lower incorrectly determines the scrollheight of the body. Use document.documentElement for IE. To make this browser agnostic, the maximum scrollheight of both body and documentElement is used.
Add Embed responsive utility
fix #12154
Merge branch 'responsive-embed' of https://github.com/boulox/bootstrap into boulox-responsive-embed

Conflicts:
	dist/css/bootstrap.css.map
	dist/css/bootstrap.min.css
fix #12007 by clarifying target of dropdown events
refactored and renamed grid mixins
fixed first element padding of list-inline
Added .list-group-item.disabled

Added support for disabled List group item.
Update variables.less
rm callout about creating .container-fluid-alikes now that .container-fluid has been added
Remove redundant :-moz-placeholder styles

No need for old Firefox versions support.
fixed two typos in carousel.less

carousel.less has two typos in glyphicon classnames. fixed them.
Docs: losslessly compress images.

Before: 25,1 KB (25.773 bytes)
After:  23,7 KB (24.352 bytes)
Compress examples screenshots with kraken.io.

Before: 1,12 MB (1.174.728 bytes)
After:  1,11 MB (1.173.614 bytes)
Sticky footers without any wrappers
Merge pull request #12465 from XhmikosR/docs-img

Docs: losslessly compress images.
Added border radiuses to table when in a panel. Fixes #12461