Pause app boot until window load event fired

Refs #17

Allows the user provided Web3 instance to be inserted before we
try to use it.

app/initializers/defer-loading.js

@@ -0,0 +1,15 @@
+/**
+ * This pauses the app's boot process until the window load event is fired.
+ * It allows the user provided Web3 instance (e.g. Metamask, Mist Browser)
+ * to be inserted before we try to use it.
+ */
+export default {
+  name: 'defer-loading',
+  initialize: function(application) {
+    application.deferReadiness();
+
+    window.addEventListener('load', function() {
+      application.advanceReadiness();
+    });
+  }
+};