Show popup onclick rather than onmouseenter

I replaced the ng-mouseenter directive with a ng-click directive since I find it annoying when a popup shows up immediately after the mouse enters the comment count link. Since it is a link I think it's more natural to show the popup after clicking the link.

I also tried implementing a timout for the mouseenter directive, but I ran out of time.

Thought: Maybe this behavior can be toggled via configuration option from the backend. But it seems a bit oversized for such a small and simple module.