Register models in admin based on settings supplied

[benvand]

In billing/admin.py
is there a reason that all those models are blanket registered with the admin?
Could this not be based on settings? Something like

for key in settings.MERCHANT_SETTINGS:
    admin.site.register(key_model_dict['key'])

[tuxcanfly]

I think we can remove the admin registration altogether. One can add them through their app's admin.py if required.