Remove "All time" link from Universal Analytics

* Was expensive
* This is just a removal of the link; appending `period=all-time` to a
  Universal Analytics URL query will still, at present allow you to *try* to reach it.
 
We *could* 400 Bad Request it, but that would involve *adding* code; UA/All time requires no special code over and above what exists for other areas, so there's nothing to remove as such.
Yep - moved to an option on `.all`. I don't want this stuff in the controllers if we can avoid it - it'd have to go in six places and the logic to decide whether we're rendering universal views is already in the views. To avoid that larger issue while still getting the slug knowledge out of the view, it's a method only.