Allow addon/ to contain any known JS filetypes.

This allows usage of `*.coffee` (or any other `js` type preprocessor).
Merge pull request #2054 from rwjblue/allow-addons-to-handle-all-types

Allow addon/ to contain any known JS filetypes.
Merge pull request #2057 from rwjblue/use-ember-env-properly

Ensure window.EmberENV uses the EmberENV key from config/environment.js.
Do not use inline script tags.