* Adding **user fixtures** for signin
* 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.
* Added **route 'login'** on url '/ghost/ember/signin'
* Added authenticated route with an error hook that redirects to the login route, if status 401 (unauthorized) is returned from REST API.
* All "secure" routes now extend from authenticated route
* Add /ghost/ember to noAuthNeeded routes in middleware
- Change fixture response of posts route to actual format.
- Extracted classNames logic of routes into style-body mixin.
- Additionally replaced all double-quotes with single-quotes for style conformance.
