Added Test for hasMany through association

Added a contrived Author model to Comment. This causes Comment to
have two belongsTo associations. One to Author, and another to Post.

The added test currently fails by timing out. I could very well be
doing something wrong as this is my first attempt at an ember data test.

I will continue to investigate as best I can, but I'm sure somone with
more skill can figure this out a lot faster than I can, even if its only
to point me in the right direction.