Add babelify transform to use ES6

[januszm]

I'm still quite new to this gulp world so feel free to modify this PR (or send me some instructions on how to improve it). There are no tests for this change. I was able to test on one of my React JS apps and works fine, it allows using the below as an example:

import { Router, Route, hashHistory } from 'react-router'

[randylien]

Thanks for your PR, but browserify's transform config is defined in _package.json.
Maybe we don't need to require it again in gulpfiles.js.