Fixed awkward indentation in admin URLconfs
Added AdminSite attributes for easily changing admin title.
AdminSite now has overridable site_header, site_title and index_title attributes. Changed
each admin view to pass these to the context (in a new AdminSite.each_context() method).
The intent here is to make it easier to override these things in the common case, instead of
having to override a template, which is a bigger burden.