added basic user authorization

@RichardBlair 
Updated routing, controllers, and views in adding user authentication to dickbook to match Rails 4.1.1 standards utilizing information from the following resources:

http://railscasts.com/episodes/250-authentication-from-scratch
https://github.com/rails/strong_parameters
and, of course, advice from https://github.com/RichardBlair
I would say don't put the `logged_in?` method here, you can actually put that in the ApplicationController.
So in ApplicationController do:
```
def logged_in?
  !!@current_user
end
```