HG-257: Top contributors tracking

There are two issues at hand here and this PR addresses only one of them.

First the way we handle links seems to prevent the action from firing. The "workaround part is to set the tracking" label as data attribute in DOM and then fire the action when the link is handled.

Unfortunately this solves only half of the issue. As these are outbound links, there is a good chance that the event will never hit the tracking backend as the HTTP request are reset as @hakubo pointed out. I see there is a solution to this issue (https://support.google.com/analytics/answer/1136920?hl=en) in universal analytics, which we currently don't use. 

:crying_cat_face: