Comment system on hack details page

Created a comment submission form and list of comments on the hack details page. Added one field to the Hack mongoose model that is a list of objects representing the comments. Hack details page fetches comments from the database and renders them on the page. 
![Screen Shot 2013-02-10 at 3 30 26 PM](https://f.cloud.github.com/assets/1041597/143957/e7734592-73d9-11e2-9cc7-bcedb1c8ec75.png)