Merge pull request #10 from mattThousand/like_a_movie

Like a movie
remove link to like movie if user is unauthenticated

- create like_link helper method
remove like link from review show page

- move like_link helper to application helper
add authenticate_user! to likes controller
- Add user_id to likes table
- Add user validation to like model
- Create db association for like
- Add likes association to user model
- Add dependent destroy for likes on user model
- Add single like per user functionality
- Define already_liked_by? method in movies_controller
- Add already_liked_by functionality added to reviews
- Add already_liked_by to application_helper