Convert CommonJS exports to ES6-compatible exports

We use `export default` begrudgingly here. Ideally we'd use just `export`, though this entire SDK expects things to be exported as a default. Instead of breaking everything, we'll sacrifice our export pattern for a smaller diff - a later commit can always do the default export -> regular export conversion.

src/components/structures/auth/Login.js

@@ -54,7 +54,7 @@ _td("General failure");
 /**
  * A wire component which glues together login UI components and Login logic
  */
-module.exports = createReactClass({
+export default createReactClass({
     displayName: 'Login',
 
     propTypes: {