Adding user fixtures for sign-in
Adds an initializer for the current logged in user.

The created singleton object is injected into all controllers + routes.
It can be used inside routes + controllers with this.get('user').

For simple development the object is instanciated with a userFixture.
Once a proper login and api mock is in place, the fixture needs to be removed.
Add login

* Added route 'login' on url 'sign-in'
* Added authenticated route with an error hook that redirects to the login route, if status 401 is returned from REST API.
* All "secure" routes now extend from authenticated route
* Add /ghost/ember to noAuthNeeded routes in middleware