WIP: Bootstrap 3 (SASS)

**Reference**

https://github.com/twitter/bootstrap/pull/6342 3.0.0-wip Pull Request


---
This PR should have all changes including this commit https://github.com/twitter/bootstrap/commit/7cbb1c0452a1d9904f7655aea78644def85b7f2e

Let's do the last steps until the final release together. To ship this translation as fast as possible when bootstrap releases the final 3.0.0