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
Redo the getting started section to mention BootstrapCDN
nuke line numbers
Fixes #7744: update grid mixin to use latest grid styles
no units on 0 values
no need for zero padding on navbar top/bottom; better comment
add back bottom margin to navbars
make that left/right padding, not top/bottom on navbar
outdent the rows for tablets and above
add the fade class to the default modal docs
Updating the README.md to fix the link to Bower
Merge pull request #7750 from hppycoder/3.0.0-wip

Updating the README.md to fix the link to Bower
Use @font-size-... variables instead of hardcoded font-size in px
Corrected typo in carousel.html

Changed text from "First featurette headling" to "First featurette heading" in the first `h2.featurette-heading` tag.
Use padding instead of #push with box-sizing: border-box
Fix input border flicker in Chrome from @garoevans, closes #7689
add customizer link to docs homepage
Cleanup .navbar-form styles

* Nuke the commented out navbar forms code that's not currently needed
* Add a few more examples to the .navbar-form docs section
* Remove (for now at least) top padding on checkbox and radios
delete lingering navbar dividers code since we nuked that awhile back