Improve signin

Ref #2413

- Remove fixture and use actual API
- Store and send down actual logged in user data
- Refactor isLoggedIn to use computed property on application
- After signin, update user data in dependency container
- Add CSRF to all routes and controllers via initializer
- Update authenticated route to check for user.isLoggedIn
- Add notifications for signin error
- Add notifications.showAPIError helper
- Add plumbing for refreshless signup to doSignUp in admin controller