Enable Hot Module Replacement in webpack.

This allow the webbpack dev server to properly reload JavaScript modules
while running in dev without restarting the server. We need to connect
to webpack-dev-server directly because SockJS doesn't support more than
one connection on the same host/port.

static/js/common.js

@@ -1,3 +1,8 @@
+// This reloads the module in development rather than refreshing the page
+if (module.hot) {
+    module.hot.accept();
+}
+
 var common = (function () {
 
 var exports = {};