Fix all hits summary bug

* Was defaulting back to summary when selecting a time period from the "All hits" tab
* Isn't now
* Tidy up the specs while we're here to more adequately convey the intended behaviour, rather than the implementation details
It’s not entirely clear what this is doing and why unless I go and look at the page itself and figure out how it works. Given that, combined with the fact that it’s relying on the behaviour out in the controller, would it be clearer to pull this out into something more descriptive? Perhaps a method called something like `on_all_hits_page?`.