do not display clicks count in oneboxes

This follows fd035cf7772c068f6201e539bd6ef314dc76841d.

This prevents the clicks count badges to be displayed in oneboxes, except when we **explicitly** force it.

This is done by using the following condition
```javascript
if ($link.closest(".onebox-result").length === 0 || $link.hasClass("track-link")) { ... }
```
in both `post_view.js` (when the post is rendered) and `click_track.js` (when the user clicks on a link). 

I also added a few specs for `click_track` to make sure I didn't break anything.