add finally polyfill for promises

web/app/common/polyfills.js

@@ -1,5 +1,17 @@
 import 'core-js/es6/promise';
 
+// default promise polyfill doesn't include finally
+Promise.prototype.finally = function finallyFn(callback) {
+  const constructor = this.constructor;
+
+  return this.then(
+    (value) => constructor.resolve(callback()).then(() => value),
+    (reason) => constructor.resolve(callback()).then(() => reason)
+  );
+};
+
+window.Promise = Promise;
+
 export default function loadPolyfills() {
   const fillCoreJs = () => {
     if (