Credit Admin lets you change info

[akoumjian]

I'm guessing that you are not supposed to be able to edit credit objects in the admin. When you try to limit the editable fields by returning None here:

https://github.com/balanced/django-balanced/blob/master/django_balanced/admin.py#L148

You actually end up letting users edit all fields, because you are defaulting to all fields here for a None attribute:

https://github.com/balanced/django-balanced/blob/master/django_balanced/admin.py#L30