Add ES6 Support (with 6to5)

:warning: DO NOT MERGE :warning: 

- [ ] figure out if anything special is needed to get this to work with require.js
- [ ] dynamically compile es6 to es5 using [6to5](https://github.com/6to5/6to5)
- [ ] get tests to pass
- [x] don't try to test the es6 fixtures