Use Project model from EmberApp.

* Add `Project.closestSync` (we cannot do async in `Brocfile.js` right now).
* Use `Project.require` and `Project.name` logic for `EmberApp`.
* Remove boilerplate/defaulted params from `Brocfile.js`.
Merge pull request #989 from rjackson/use-project-in-ember-app

Use Project model from EmberApp.