Add a page to show delivery rates week-by-week

Implements
https://github.com/alphagov/notifications-api/pull/286

Will always show weeks as Monday to Sunday.

app/templates/components/big-number.html

@@ -26,7 +26,9 @@
   failure_percentage,
   danger_zone=False,
   failure_link=None,
-  label_link=None
+  label_link=None,
+  show_more_link=None,
+  show_more_text=''
 ) %}
   <div class="big-number-with-status">
     {{ big_number(number, label, label_link) }}
@@ -44,4 +46,7 @@
       {% endif %}
     </div>
   </div>
+  {% if show_more_link and show_more_text %}
+    <a href="{{ show_more_link }}" class="big-number-with-status-show-more-link">{{ show_more_text }}</a>
+  {% endif %}
 {% endmacro %}