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.

Fixes #1110
 * Access lastObject using a method.
 * Use string length instead of a nil check.

Hat tip @sendhilp
Merge pull request #1532 from wordpress-mobile/issue/1110-comment-notification-links

Adds support for rendering HTML in the comment view.