When generating *_id attribute for nested associations, add parent association as a dependency

E.g.:

```javascript
Model = Ember.Resource.define({
  schema: {
    address: {type: Address, nested: true}
  }
});
```

It will generate `address_id`, but if `address.id` changes, it isn't propagated to `address_id` without the changes bellow.

@jish @shajith mind taking a look?