new tests for Rules

[highpost]

I meant to respond to PRs #99 and #100 sooner, but it took a lot more work to get that done. In the end I wrote a lot of pytests to exercise the new features developed by @efficiosoft: model-based permissions and permissions derived automatically from view types. Those both look great. I really like model-based permissions.

I also wrote tests to exercise the integration between Rules and Django Rest Framework. This led to PR #105. With that in place I think you can say that Django Rules works with DRF as a permission backed envisioned by https://www.django-rest-framework.org/api-guide/permissions/#object-level-permissions. To support that I would like to submit documentation PRs for DRF to advertise that fact. I think a documentation PR for Django itself would also be helpful.

The tests are in https://github.com/highpost/rules_test and if you want to add them to Rules I would like that.