Hope there is a way to get original MSLayer through "new Group"
I followed the guiding code at [here](https://developer.sketchapp.com/reference/api/#create-a-new-group)

However, I found the value it returns is a wrapped object from which I cannot access the original MSLayer.

The wrapped object looked like this:
![image](https://user-images.githubusercontent.com/6670037/41148531-c6128bb0-6b3b-11e8-8443-b85540f06e45.png)
