John patch simple tab

This is a pull-request for https://github.com/evanxd/travis-reporter/issues/118.
* Insert some code into `index.jade` to enable `Travis-reporter` to have the `tab object`.
* Insert some code into `base.css` to decorate the `tab object` to let it becomes a "tab-like" view.
* Insert some code into `button.js` to implement the function of `toggle button`, and bind it to `tab object`.