User Sign Up

Final piece to complete: [setupCurrentUser on sign in](https://github.com/gschorkopf/frolfr/commit/e87503151b748c13150fde73f6a028c039e7a946#diff-90557946fd2d72192769084779307fb4R18). @killpack thoughts on how to accomplish this? I need to use the pieces in the SessionController.

Will finish [#18]
So, it seems to me like it'd be okay to set these properties here if we didn't have an explicit `UsersNewController` (that is, if we just had a route and relied on Ember Magic™™™ to generate the controller for us). But since we're already going to the trouble of creating our own `UsersNewController`, it seems like that controller ought to be responsible for knowing what properties it has and what the default values of those properties are.