Show screenshot age in [preview]

changedetectionio/templates/preview.html

@@ -57,6 +57,7 @@
          </br>
          {% if is_html_webdriver %}
            {% if screenshot %}
+             <div class="snapshot-age">{{watch.snapshot_screenshot_ctime|format_timestamp_timeago}}</div>
              <img style="max-width: 80%" id="screenshot-img" alt="Current screenshot from most recent request"/>
            {% else %}
               No screenshot available just yet! Try rechecking the page.