Fixed nested tab elements li activation

Added closest li instead of direct parent so that you can nest multiple elements within tabs, such as button groups
Customizer: switch to UglifyJS2 (v2.4.13).

The uglify build is generated with `uglifyjs --self -o uglify.min.js`.
Add the jquery check in customizer's output.
Add the license header in the non minified build too.
Run `grunt`.
Fix form-control-feedback position when label has sr-only class
Fix indent
added bower reference to main less file
Add documentation for using optional icons with sr-only labels
fixes #11099 - $.collapse() overrides the original dimension of the coll...
fixes #13296 Dropdown disappears with right-click on Firefox
Added specificity note to docs per issue #13332
Fixed typo and added leading space
Dropdown menu in justified button-group

It seems that dropdown-menu in justified button-group appears at the far
left of the group. Check the problem in [Bootstrap
site](http://getbootstrap.com/components/#btn-groups-justified).
Merge pull request #13358 from Jakobovski/docs-improvements-#13332

Added specificity note to docs per issue #13332
fix #13360 by making deprecation notices visible in customizer
fix #13337 by mentioning removal of .progress-* contextual classes
FIX: #13355. Added .navbar-nav to migration change list.
quote data-* attribute value in docs JS per best-practices
Merge pull request #13373 from twbs/fix-13360

Make variable deprecation notices visible in customizer