Split from MDL-73379

When browsing through the admin tree there are 3 types of pages under the hood:

1) admin settings, served by /admin/search.php

2) admin categories /admin/category.php?category=analytics

3) admin section admin/settings.php?section=analyticssite

4) admin pages, eg admin/registration/index.php

All of these conceptually are under the same admin tree so should ideally have consistent header, styling and navigation.:

a) make the title consistent. Current state sometimes it is 'Site administration' and sometimes it is the site title. It should be consistently one or the other, or possibly in some cases a more context heading based on the current location in the admin tree

b) add the admin settings search bar to all of them

c) consitent crumb trails (I think being addressed elsewhere)