Change `posts`, `post` and `signout` routes to be `AuthenticatedRoute`s

No issue
The following is a list of routes which are not authenticated
- placeholder routes: `editor` and `content`
- `application`
- password routes: `forgotten`, `reset`, `signin`, `signup`
Merge pull request #2953 from novaugust/authenticate-ember-routes

Change `posts`, `post`, and `signout` routes to be `AuthenticatedRoute`s