Dynamic Titles in Ghost Admin

Closes #4487 

- Every route can set a title token that is combined with the blog’s
title, resulting in titles like ‘Content - Test Blog’.
- Subroutes are supported (‘Settings - General - Test Blog’)
- The blog’s name is applied to and taken from the `config` object to
spare Ember a REST call via `store.find(‘settings’)`.
- Tests have been changed to test for the new titles.
- The initially proposed solution
(https://github.com/paddle8/ember-document-title) doesn’t play nice
with EAK, which is why I went with this solution
(https://gist.github.com/machty/8413411) by Ember.JS core dev @Machty.
Should be `User`, singular?