Update the plugin/app_hook/menu tutorial

Update the plugin/app_hook/menu tutorial.

The django-CMS 3.0+ tutorial requires its readers to follow along using a tutorial from Django 1.2 (which is no longer supported by django-CMS 3.0+), which creates issues for users learning the CMS.

This PR updates the tutorial to instead require the user to follow the same tutorial from the Django 1.6 tutorial and is updated accordingly.