User managment screen, first pass

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 :slug as a URL parameter
- updated labels everywhere (from "user" to "users")
- updated "profile" link to header to point to proper "users/:slug" route
- updated core/client/.jshintrc to recognize moment as a valid global function
- adjusted DOM selector used in Casper to properly identify the new screen
- added "slug" as a new property of the user data used during the Casper functional tests
We have a file in `/utils` that has reusable moment functions. Might be nice to put this in there as well, so that we have one central point for `moment` use