Don't start the meat of the app until the inspected page is ready

The inspector reloads the page with the backboneAgent injected, so we
need to wait until the page is re-loaded to begin our inspector app.
Actually - what if we do something cool... and proxy the event


```js
this.listenTo(this.inspectedPage, 'ready', function () {
  this.trigger('page:ready');
});
```

This way, we can listen for a client event in the app.

```js
this.listenTo(this.client, 'page:ready', ...);
```