- added utility methods `lookupModel` and `lookupStore`
- `data.Collection`
   - added `add` and `remove` events
   - added listener for `data.Model` `sync`, specifically for when a model is created to replace its phantom id with its real one
- `data.Model`/`data.Schema`
   - adding `stringify` to a schema property now tells a model to skip adding it the return object of a `toJSON` call
   - fixed issue with utility method `lookupModel`