Improve CoffeeScript support

Additions
- New folder for CoffeeScript related files
- Make grunt-neuter play nicely with CoffeeScript


Before we merge, there are two slight problems.
- I tried to set the [default option for CoffeeScript](https://github.com/fayimora/generator-ember/pull/new/coffee-script-support#L0R82) but it doesn't seem to work. How do I make the default to be NO so users don't have to explicitly specify? I expected `default: 'y/N'` to work but it did not.

- If you select CoffeeScript and run `grunt server`, nothing shows up on the webpage. You have to re-load `app.coffee` first. This is only because the `grunt-neuter` task runs before the `coffee:app` task which is obviously stupid. So how do I 'force' `coffee` to run before `neuter` on initial launch?

Cheers

cc @passy @inkredabull