feat($resource): expose $promise and $response in promise-based api

This is a WIP to show a possible $resource promise-based api discussed in https://github.com/angular/angular.js/commit/dba6bc73e802fdae685a9f351d3e23c7efa8568a

Main changes:
 * ```$promise``` and ```$response``` (http response) are exposed on resource instance object in addition to ```$then``` and ```$resolved```.
 * on success, the promise resolves to the same resource instance object filled with data. This is as expected to enable using it in resolve section of ```$route.when()```.

Arguably, ```$then``` and ```$response.resource``` are not needed anymore, what do you think?