This change accomplishes 3 things related to the `defaults` member for models. First, it fixes up the typing for the `defaults` definitions in all the models that we've implemented so far to be `Result<Partial<AttrsType>>`. Second, for things that inherit from base classes, we now rely on automerge instead of manually calling `_.defaults()`. Finally, we had a few instances where the defaults were including objects or arrays but were implemented as a plain object instead of a function. We've had problems in the past where these weren't deep copied, and multiple objects ended up sharing the same object or array value. These have been fixed up to always be a function that returns new data. Testing Done: Ran js-tests.