Fix flickering on progress bar width update

Issue visible on lastest version of Chrome Browser (if you update progress bar width from 100% to 0%) -> flickering appears

Fixed with addition of .backface-visibility(hidden) mixins
update docs
Update justified nav CSS for proper selectors
recompile after last justified nav tweaks
Fixes #7721: change @navbar-text to @navbar-color, along with inverse options
Fixes #7511: add support for nested button groups so you can use dropdowns in your button groups
Merge pull request #7621 from jeremydenoun/patch-1

Fix flickering on progress bar width update
use @screen-small var in grid.less

Per comment by @nextgenthemes on/in cd06c5baac64a366
Merge pull request #7782 from cvrebert/patch-1

use @screen-small var in grid.less
Fixes #7783: nuke bottom margin on fixed-bottom-navbar
Merge branch '3.0.0-wip' of github.com:twitter/bootstrap into 3.0.0-wip
correct right nav in navbar examples