* Identify code that needs to be pulled out of/removed from compat.py
* Extract modern code from get_names_and_managers in compat.py and remove compat code
* Extract modern code from is_authenticated() in compat.py and remove.
* Extract modern code from is_anonymous() in compat.py and remove
* Extract modern code from get_related_model() from compat.py and remove
* Extract modern code from value_from_object() in compat.py and remove
* Update postgres compat
JSONField now always available.
* Remove DecimalValidator compat
* Remove get_remote_field compat
* Remove template_render compat
Plus isort.
* Remove set_many compat
* Remove include compat
