* merge master into v3
* fix order_by snake casing by checking if value is None, switch executor to execution_context_class since schema.execute no longer supports executor
* fix linting by removing duplicate defintion and test of convert_form_field_to_string_list
* Reset the global registry after each test (teardown)
* Create a settings fixtures that returns graphene_settings and resets
the graphene_settings after use (teardown)
* Convert test_mutation tests from unittests.TestCase to pytest
* Convert test_mutation PetType to a pet_type fixtures that reregisters
the type
