Update the plugin/app_hook/menu tutorial

Update the plugin/app_hook/menu tutorial from Django 1.2 (which is no longer supported by django-CMS) to Django 1.6's tutorial.
Merge pull request #2985 from mkoistinen/update_tutorial

Update the plugin/app_hook/menu tutorial
Update graphic and supporting instruction for django-CMS 3.0
Merge pull request #2986 from mkoistinen/update_tutorial

Update graphic and supporting instruction for django-CMS 3.0
More updates for the cms extending tutorial
Merge pull request #2987 from mkoistinen/more_doc_updates

More updates for the cms extending tutorial