Create favorites controller

- Function as primary controller for one-page app
- Index, create, destroy methods only
Add sessions controller

- Responsible for authenticating user
- Setting session for visitor and attaching to favorites
Add sessions controller to login/logout registered users
Remove user authentication from users model.

- Re-enable protect_from_forgery
Refactor routes

index view is now favorites#index
- favorites
- sessions
- users
- messages