Put the download csv link on the activity page.

Still needs some tests, probably some refactoring as well.

app/templates/views/notifications.html

@@ -43,7 +43,11 @@
       <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
     </form>
   {% endif %}
-
+    <p class="bottom-gutter">
+       <a href="{{ download_link }}" download="download" class="heading-small">Download this report</a>
+       &emsp;
+       Data available for 7 days
+    </p>
   {{ ajax_block(
     partials,
     url_for('.get_notifications_as_json', service_id=current_service.id, message_type=message_type, status=status, page=page),