Add support for DRF (Django Rest Framework)

[codingjoe]

DRF's ModelSerializer has a fixed mapping for Django model fields. Our custom fields are of course not in there which means they are not identified which can lead to strange and unexpected behavior. https://github.com/encode/django-rest-framework/blob/5e6abfbafebd7eed8ece110b8c32949f88e94e9d/rest_framework/serializers.py#L838-L863

I would suggest to add contrib.rest_framework that provides a subclass of the ModelSerializer that adds support all the Salesforce fields.