Adds Broccoli and moves current code to ES6

Instead of Grunt, we're moving towards Broccoli for building and
testing. It's simpler and is being embraced by Ember itself.

This commit makes all tests pass with Broccoli as server. Plus, code is
now using ES6 modules.
Clean up unneeded loader files
Building distribution with Broccoli.js

This also improves the README.md, although the instructions haven't been
tested yet.
Minifying using Broccoli
Removes Grunt
Merge pull request #26 from kurko/port_to_es6

Adds Broccoli and moves current code to ES6