Add Airtable demo

app/javascript/demo.js

@@ -13,8 +13,13 @@ document.addEventListener("turbolinks:load", function () {
     var name = document.getElementById('demo-submission-name');
     var demoFields = document.getElementById('demo-fields');
     var demoSucess = document.getElementById('demo-success');
+    var demoIframe = document.getElementById('demo-sheet');
     demoFields.style.display = 'none';
     demoSucess.style.display = 'block';
     name.innerText = e.detail.submission.Name;
+    // The airtable sheet must be reloaded for the submission to get visible
+    if (demoIframe.dataset.refresh) {
+      demoIframe.src = demoIframe.src + '&c=' + new Date().getTime();
+    }
   });
 });