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, I'm thinking that instead of making this controller do the authorization stuff, we ought to just be able to trigger the login action on the `SessionsController`, so we don't duplicate logic.

So I'd replace this whole `Ember.$.post` block with something like:
```javascript
this.controllerFor('sessions').send("loginWithCredentials", email, password);
```
(You'd need to add `needs: "sessions"` to the top of this controller definition to be able to do this.)

And then expose an action in `SessionsController` like:
```javascript
loginWithCredentials: function(email, password) {
  this.set('email', email);
  this.set('password', password);
  this.send('login');
}
```

Something like that? Not sure if this will work exactly like I hope it will, but that's my instinct.