Adds support for rendering HTML in the comment view.

 * Note model can now return the comment HTML (previously all HTML was being stripped).
 * CommentView will now render HTML links and images.
 * CommentViewController and NotificationsCommentDetailViewController both now support tapping/viewing links to a web view.
 * Also added some CSS styling to get blockquotes looking better.

Before:
![ios simulator screen shot apr 3 2014 11 33 31 am](https://cloud.githubusercontent.com/assets/789137/2609118/66e2ad64-bb72-11e3-8a2a-e623a45cb30d.png)

After:
![screen shot 2014-04-03 at 10 55 02 am](https://cloud.githubusercontent.com/assets/789137/2609121/71439c78-bb72-11e3-9a59-1b75abd12c6b.png)


Fixes #1110