Link back to all template versions from 1 version

If you get linked to a single version of a template, you’re at a dead
end. Let’s add a link to go back up a level to where you can understand
the current version in context.

app/templates/views/templates/template_history.html

@@ -19,4 +19,9 @@
     {% endwith %}
   </div>
 
-{% endblock %}
+  {{ page_footer(
+    secondary_link=url_for('.view_template_versions', service_id=current_service.id, template_id=template.id),
+    secondary_link_text='See all versions of this template'
+  ) }}
+
+{% endblock %}