Saleor: Use Django's JSONField instead of external package

[Pacu2]

Since v1.9 Django comes with builtin JSONField, we could start using it instead of an external jsonfield package.

Potential drawbacks:

• It's PostgreSQL-specific field
  But we are supporting only PostgreSQL + HStoreField(postgres-specific as well) is already in use

Docs:
https://docs.djangoproject.com/en/2.1/ref/contrib/postgres/fields/#jsonfield

[patrys]

We already use django.contrib.postgres extensively, including using PostgreSQL-specific hstore format.

[the-bionic]

Hello. How can I help with this?

[Pacu2]

Hi @the-bionic,
We are currently getting JSONField field from the jsonfield package.
We are eventually looking to drop this package, and use JSONField from django instead as defined in https://docs.djangoproject.com/en/2.1/ref/contrib/postgres/fields/#jsonfield

Pull request is more than welcome!

[the-bionic]

Great. I will work on this.