Fix parent object loading when calling ready() on object chains with new models.

I've been running into an issue where parts of the javascript code create a
review object, then create a comment. The hierarchy here goes RB.ReviewRequest
-> RB.Review -> RB.<comment type>. Calling ready() on the comment will fail
to load the ReviewRequest, which means that the Review won't have a valid url.
Fix up some problems with the ReviewReply model

There were a couple issues with RB.ReviewReply from my previous implementation.
First, I had used underscores in the property names instead of using camelCase.
This involved some changes to the plumbing but is less than I had expected.
Second, the _.defaults call wasn't passing in the correct prototype defaults, so
the resulting object didn't have some of the right attributes.