[#73271184] Style favicons

- Refactoring `.icons` & `.favicons` in `docs.scss`
- Do `scsslint` while `grunt dev` task
- Add favicons style

![screen shot 2014-07-22 at 6 05 56 pm](https://cloud.githubusercontent.com/assets/228359/3655861/6f5967d6-117f-11e4-896f-2c81af25b189.png)