Django OAuth Toolkit v2

Django OAuth Toolkit is available in version 2 and we need to update. Sadly its breaking a few features we are using and we need to do this later and deprecate the features now.

At least oob support is dropped, which is a problem for all of our headless clients and eventually third party clients as well. In order to fix this, we should implement Client Authentication Flow, which enables headless clients to consume our APIs and is already supported by django-oauth-toolkit. At the same time we can deprecate OOB and remove it later, which allows us to update the Django OAuth Toolkit.