Remove -webkit-backface-visibility on skew mixin

Ref #5319 - This rule is causing pixelated edges on iOS. Removing
it makes everything smooth across all OS's, browsers, and devices.
Update carousel-caption btn styles
Add carousel indicators to example
Additional cleanup to responsive navbar
updated links on homepage
more link fixing
button for navbar toggle
add type attr
only negative indent nested grid rows; add new grid example
Docs examples update

* Remove unused fluid image
* Add image, link, and description for new grid example
* Update sign in example image
Merge branch '3.0.0-wip-carousel' of https://github.com/burnsra/bootstrap into burnsra-3.0.0-wip-carousel
run make
Fix responsive view for inverted navbar example
Fix link to navbar doc
Fix corss link for sticky footer
Replace png img by holder.js in carousel example
remove unused img from previous commit
Improve responsiveness for tablet and below of navbar in carousel example

- Remove margin-top of navbar-wrapper
- Remove border radius of navbar
- Space out the carousel
Merge pull request #7453 from burnsra/3.0.0-wip-nav

Fix responsive view for inverted navbar example
Fixes #7462: add radial-gradient spec to mixin