Return/resolve actual newly created/updated item from store

We are returning the actual newly created/updated item as returned from store. Best explained with an example: If we pass `{name: 'dojo'}` to `store.newItem()`, then we might get something like `{id: 99, name: 'dojo', 'date_created': ...}` returned from well-built REST server. Now that we have a deferred/promise here (since last commit), we would expect the resolved value to be the new value (as in `item`) returned from server (or whatever returned by the store), but not our original input (as in `object`). Without this fix, data consumers may get incomplete object which differs from actual store structure.