feat(angular-resource): patch resource to add promise support

Resources generated via $resourceFactory offer a $promise variable
now. That variable may be used to return a promise that is evaluated
with the loaded resource once loading is finished.

It allows us to perform things like

somePromise.then(function() {
  return MyResource.query({ id: 'foo' }).$promise;
});
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
Merge branch 'master' of github.com:camunda/camunda-bpm-platform