Fix direct access to settings/user

closes #3162
- removes injection of user object in application route's beforeModel
- removes injection/cleanup of user object in signedIn/signedOut actions
- removes loading of user and passing to signedIn action in signup/setup controllers
- adds 'user' property to session object
- updates header nav to reference session.user
- sets model of settings/user route to session.user and forces reload
- on leaving settings/user, rollback any unsaved changes
Merge pull request #3174 from kevinansfield/session-user

Fix direct access to settings/user using session.user CP
Removing old "user settings" screen and putting in new MU "users settings" screen.

Fixes #3078
- new "users" route, with matching controller and template
- fetching real data from /ghost/api/v0.1/users/
- updated "user" route to accept a :user_id as a URL parameter
- updated labels everywhere (from "user" to "users")
- update "profile" link to header to point to proper "users/:user_id" route
Adjusting functional tests for new "users settings" screen

fixing validation failures:
- adjusted DOM selector used in Casper to properly identify the new screen
- updated core/client/.jshintrc to recognize moment as a valid global function