a few changes to make A/B testing easier

app/templates/error.js

@@ -0,0 +1,12 @@
+const html = require('choo/html');
+const assets = require('../../common/assets');
+
+module.exports = function(state) {
+  return html`
+  <div id="upload-error">
+    <div class="title">${state.translate('errorPageHeader')}</div>
+    <img id="upload-error-img" data-l10n-id="errorAltText" src="${assets.get(
+      'illustration_error.svg'
+    )}"/>
+  </div>`;
+};