Assignment 4 Complete!

- Added comments to the link's show page
- Changed the login requirements a little so that only registered users can change links/comments, but anyone can look at them
- Only the user who made the link/comment can delete/edit it
- Upvoting/downvoting comments affects the cumulative score of a link
- Added the integration tests

That should be everything, and it all worked really well in the browser. Let me know if I'm missing anything!