Bug 847982 paginate comments on report list

@AdrianGaudebert r?

Now you get pagination on the Comments tab of report list too. 
It's not a brilliant solution because the contents of the Comments tab is loaded with AJAX and ideally, when you click to go to a different page it should just reload that piece of AJAX. However, it gets non-trivial about how to change the main URL (pushState?) and besides, it's rare that people go to page 2 or 3 so this'll do.