Docs: create new callout classes
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
Update customizer

Add all the new things to customizer:
* `@headings-font-family`
* `@container-*`
* darker `@btn-default-bg`
Merge pull request #8478 from juthilo/3.0.0-customizer

Update customizer
Merge remote-tracking branch 'upstream/3.0.0-wip' into 3.0.0-wip
fix broken scrollspy example
Merge branch '3.0.0-wip' of github.com:twitter/bootstrap into 3.0.0-wip
Add missing backtick in comment
remove webkit-overflow-scrolling from modal for now /cc #8495
Merge pull request #8498 from cvrebert/patch-1

Add missing backtick in comment
remove margin from left side of navs since it's no longer being set
Merge branch '3.0.0-wip' of github.com:twitter/bootstrap into 3.0.0-wip
Merge remote-tracking branch 'upstream/3.0.0-wip' into 3.0.0-wip
Remove changelog in favor of GitHub releases
Update readme to point previous releases to GitHub project releases (fixes #8508)
Fixes #8356: Move browser compatibility from wiki into real docs
Move license FAQs to the docs, add link to side nav
Fixes #8360: Add mention of IE compatibility mode to docs
maybe fix this old ass issue #5973
rebuild doe