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
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).
emphasize that bootstrap-rtl.css & bootstrap.css should not be used together
Fix .visible-print deprecation version #.
tweak formatting in Carousel docs for clarity; fixes #13522
unlock & bump grunt-jscs-checker to ~0.4.3
Merge pull request #13528 from twbs/unlock-jscs

unlock & bump grunt-jscs-checker to ~0.4.3
Merge pull request #13504 from Quy/resputil

Fix .visible-print deprecation version #.
Merge pull request #13499 from twbs/clarify-rtl

emphasize that bootstrap-rtl.css & bootstrap.css should not be used together
move rtl to getting started, per @cvrebert's feedback
move Grunt info from README into HTML docs

Fixes #13470
Merge pull request #13531 from twbs/grunt-html-docs

move Grunt info from README into HTML docs
Update .travis.yml
Remove outdated rtl nav links
Merge pull request #13536 from Quy/master

Remove outdated rtl nav links
Fixed affix-bottom positioning

Set top position to (scrollHeight - this.$element.height() - offsetBottom).
grunt dist
Customizer: make utilities.less inclusion mandatory

Fixes #13305.
Merge pull request #13543 from twbs/fix-13305

Customizer: make utilities.less inclusion mandatory
add role="tablist" to .nav-tabs in examples to improve accessibility

Per https://github.com/paypal/bootstrap-accessibility-plugin#tab-panel
Credit: https://github.com/paypal/bootstrap-accessibility-plugin