Hits css whitespace cleanup
Make switching between hits periods easier

* Dispense of the drop down, use a tertiary navigation pattern based on
bootstraps navbar
* Works without JavaScript
* Makes time period options clearer and is a better indication of which
is selected
* On mobile/thin page widths it makes use of the collapsible menu
pattern as used in the page header
Improve semantics of hits summary page

* Improve page outline
* Elaborate on meaning of certain links using hidden text
* Add a header for the time period switcher
* Add a header for the hits section
* Make following summary sections one header level lower
Rename hits drop down partial

* It’s no longer a drop down
Include individual dates in time period selector

* When clicking a point on a hits graph you can filter the view by that
date. The date wasn’t showing.
Merge pull request #269 from alphagov/hits-no-js

Make switching between hit periods work without JavaScript