HTML for Nested comments

[Yangshun Tay]

Bootstrap supports nesting of media objects. They should be done this way instead: http://getbootstrap.com/components/#media-list.

The current HTML for comments does not have the nested hierarchy and uses div rather than li. We can be more semantic (:

Using Bootstrap's way, there's more obvious indentation of the inner comments and comments which are actually replies will be made more obvious.