Add a message if there are more than 50 rows

Similar to how we do it on the check page, we should indicate if there
are more results than we can show. No-one’s really complained about the
absence of this, but it can’t hurt.

app/templates/partials/jobs/notifications.html

@@ -50,6 +50,12 @@
     {% endcall %}
   {% endcall %}
 
+  {% if more_than_one_page %}
+    <p class="table-show-more-link">
+      Only showing the first 50 rows
+    </p>
+  {% endif %}
+
 {% if notifications %}
   </div>
 {% endif %}