Idea: include abstract models and helper functions for easier CIM

Thoughts on this:

1. Include `BaseCustomerProfile` and `BaseCustomerPaymentProfile` abstract models ([based on this](https://github.com/treyhunner/django-authorizenet/blob/c80d0f847df9bb00e9e2ac80ff9e9314451371f7/sample_project/samplestore/models.py)) with `authorizenet` app with sane default fields

2. Include helper functions that create a customer profile and payment profiles on Authorize.NET and create the corresponding models on success.