ModelAdmin - added a model_modified hook for full CRUD support
I added a simple hook called model_modified that is called after each insert, update, and delete via the ModelAdmin class. There are times when it's useful to know when a model changes in any way by the user (via the admin app), including delete. The current methodology of overriding the save_model hook does not include delete. The usefulness of this hook over using the model signals for model changes is that you have access to the response object. I used this hook to clear certain session variables that were dependent on the correlating models.