Move examples out of the main repo to twbs/bootstrap-examples

While examples are phenomenally useful and awesome for folks getting
started with Bootstrap, they don't really shine as well being buried in
the main docs. Moreover, having anything that's not core HTML, CSS, JS,
or documentation in the main repo seems to just get in the way.
Therefore, examples gets its own repo.

Specifically, we're doing the following:

* Deletes all example screenshots
* Deletes example layout
* Deletes example files
* Updates Getting Started docs to include only the template and a link
to the new examples project

All the examples and their history will be preserved in the switch.
Docs: create new callout classes
Update mixins.less

Add a the function .make-small-column. See also http://stackoverflow.com/a/17308128/1596547
Adjust info callout, add callouts to docs

* Adjust the background-color of bs-callout-info to match danger and
warning in tone
* Convert all the callouts
* Change some callouts to info/warning
* Add new callout
Tooltip: apply position class before positioning
Remove unneeded prefixes

Per caniuse, prefixes for transitions and transforms can be reduced to just `-webkit` and `-ms`. http://caniuse.com/#search=transform
http://caniuse.com/#search=transition
Carousel no longer dependent on glyphicons

Used laquo/raquo for control buttons
Updated docs
extract .alert-variant mix-in
more nesting in button-groups.less
more nesting in navs.less
extract .label-variant mix-in
extract .progress-bar-variant mix-in
Merge pull request #8404 from cvrebert/alert-variant

extract .alert-variant mix-in
Merge pull request #8405 from cvrebert/button-groups-nesting

more nesting in button-groups.less
Merge pull request #8406 from cvrebert/navs-nesting

more nesting in navs.less
Merge pull request #8407 from cvrebert/label-variant-mixin

extract .label-variant mix-in
Merge pull request #8408 from cvrebert/progress-bar-variant-mixin

extract .progress-bar-variant mix-in
more nesting in buttons.less
more nesting in navbar.less
use nesting more in pagination.less