Add live validation to password reset

Adds a new React factory for that page to handle the logic. Also
cleans up the UI a little (centers it, stops using serif font, etc).

common/static/js/src/ReactRenderer.jsx

@@ -1,7 +1,10 @@
-import 'babel-polyfill';
 import React from 'react';
 import ReactDOM from 'react-dom';
 
+// babel-polyfill must be imported last because of https://github.com/facebook/react/issues/8379
+// which otherwise causes "Objects are not valid as a react child" errors in IE11.
+import 'babel-polyfill';
+
 class ReactRendererException extends Error {
   constructor(message) {
     super(`ReactRendererException: ${message}`);