Add alternative header layout

This adds a new layout alternative that allows for search on the
left of the header and navigation items on the right to support
some layouts seen in whitehall pages.

It also corrects a stray div that was breaking the with-nav option
without a searchbox.

app/views/govuk_publishing_components/components/_layout_header.html.erb

@@ -44,10 +44,10 @@
     <div class="govuk-header__container <%= width_class %>">
       <div class="gem-c-layout-header__logo govuk-grid-column-two-thirds">
       <%= render "govuk_publishing_components/components/layout_header/header_logo", public_environment: public_environment, environment: environment, product_name: product_name %>
+      </div>
       <div class="govuk-header__content gem-c-header__content">
         <%= render "govuk_publishing_components/components/layout_header/navigation_items", navigation_items: navigation_items  %>
       </div>
-      </div>
       <% if search %>
           <div class="govuk-grid-column-one-third gem-c-layout-header__search">
             <%= render "govuk_publishing_components/components/search", {