Generalise the :all_hits_all_time task to just :view

* Can then accept params, e.g.
   `rake benchmark:hits:view[hmrc,summary,last-30-days,10]` or
   `rake benchmark:hits:view[hmrc,redirects,all-time,10]`
   `rake benchmark:hits:view[ofsted,hits,all-time,10]`
* Given no params, defaults to Ofsted, all hits, all time