resource id field should be based on serializer lookup_field

[AndreiHondrari]

Currently if you have a lookup_field on serializers that is different from the 'pk', you will be able to do `/api/objects/{new_lookup_field}' but in the payload the "id" will still be the numerical one that django uses by default. This goes for GET and PATCH. I think this is an inconsistency.

[AndreiHondrari]

I started implementing something like this over here .

The changes that are covered:

• primary resource object ID replace
• included resource object ID replace

Still to do:

• relationship object ID replace
• tests to cover some not-happy flows

[sliverc]

I think #155 also addresses this issue and there is an open PR #409

Closing this issue to focus on #155 If you think this is a different issue though please comment.