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/RoomDirectory.js

@@ -38,7 +38,7 @@ function track(action) {
     Analytics.trackEvent('RoomDirectory', action);
 }
 
-module.exports = createReactClass({
+export default createReactClass({
     displayName: 'RoomDirectory',
 
     propTypes: {