[RFC] Module transpiler update

This is a proof of concept for updating ember-data to use the latest ES6 module transpiler. It does not integrate with the existing Broccoli build system, but the final version would need to before merging. To test this, run:

```
$ node mttest.js
```

That will build `out.js` which is equivalent to `dist/ember-data.js` from the regular build. I ran the tests against this build by doing this:

```
$ mv out.js dist/ember-data.js
$ npm test
```

It seemed to work! I haven't really dug into what the difference in file size or performance might be. Perhaps @stefanpenner would like to try his hand at that?