Convert code from CoffeeScript to JS

I'm opening this PR for discussion/review of the CoffeeScript -> JS conversion.

So far I've gone over each file and tidied up the code, removing unnecessary "mess" that CoffeeScript generated, and where appropriate used native functions/lo-dash. (Note: lo-dash use is actually limited, so there could be an argument for removing it altogether).

There's probably a lot more tidying that can be done, but for now it's a good base for further development.

Tests all pass (which have also been converted to JS), and manual testing also passes.

Over to you for your thoughts @makeusabrew.
@makeusabrew Nope. If a key exists in the group container object, it will copy it to the container object overwriting any existing value. So for now, this behaves as expected.

I personally like this feature and use it in my decking.json. Where it gets fuzzy is when you have loads of key/value pairs, live environment variables. They're an array at the moment so it just overrides. Maybe we could convert that to an object to _.assign recursively?