Normalise heading sizes

Since we added template folders the templates page has had a ‘medium’
sized heading, where other pages have stuck with a ‘large’ size.

This commit rationalises the decision around which pages have which
heading size:
- ‘navigation’ pages (eg templates, team members, email reply to
  addresses) have medium sized headings
- transactional pages (ie ones which have a green button) keep the
  larger heading size

app/templates/components/folder-path.html

@@ -8,7 +8,7 @@
   link_current_item=False
 ) %}
   {% if show_fallback_page_title %}
-    <h1 class="heading-large">
+    <h1 class="heading-medium">
       {{ fallback_page_title }}
     </h1>
   {% else %}