[NG] Class含義

1. fa:Font Awesome(http://fortawesome.github.io/Font-Awesome/icons/)
   1. fa fa-tw:空白

2. btn:button (http://getbootstrap.com/css/#buttons)

   1. btn btn-danger

3. clearfix(清除浮動 換行)

   1.  clearfix visible-xs (手機)