Duplicates in api response after every data dump

[sbs2001]

After first import

(venv) shivam@shivam:~/coding/opensource/vulnerablecode$ curl http://127.0.0.1:8000/api/packages/?name=python-django
{"count":2 ..............

After second import

(venv) shivam@shivam:~/coding/opensource/vulnerablecode$ curl http://127.0.0.1:8000/api/packages/?name=python-django
{"count":4...............

This is critical. We probably need to enforce more constraints on our models.

[haikoschol]

Looks like a duplicate of #28, but I haven't dug into either one in detail to understand whether there are differences. In general our import process produces lots of duplicate rows which needs to be fixed. I hope to achieve that in one central place (instead of writing code to fill the DB in every importer) in #152.

[sbs2001]

Duplicate of #28