Re-ordered the Product fields on the edit form.

This is done with by registering Product with a model admin object `ProductAdmin`.
Split the form up into fieldsets.
Added two inline objects to display related images.
Added two inline objects to display related reviews.
Renamed the field.
Modified datetime field and overrode `Review.save`.

Abandoned the `auto_now_add=True` attribute of `created_on`, refer to [django-auto-now-and-auto-now-add](http://stackoverflow.com/questions/1737017/django-auto-now-and-auto-now-add) .

The override of `Review.save` updates the timestamp on save.
Modified the display of field members.