Convert Meta classes to new-style classes

common/djangoapps/course_action_state/managers.py

common/djangoapps/course_action_state/models.py

common/djangoapps/course_modes/admin.py

common/djangoapps/course_modes/models.py

common/djangoapps/django_comment_common/models.py

common/djangoapps/embargo/forms.py

common/djangoapps/embargo/models.py

common/djangoapps/external_auth/models.py

common/djangoapps/student/admin.py

common/djangoapps/student/models.py

common/djangoapps/track/backends/django.py

lms/djangoapps/ccx/models.py

lms/djangoapps/certificates/models.py

lms/djangoapps/shoppingcart/models.py

lms/djangoapps/verify_student/models.py

openedx/core/djangoapps/course_groups/models.py

openedx/core/djangoapps/user_api/accounts/serializers.py

openedx/core/djangoapps/user_api/models.py

openedx/core/djangoapps/user_api/serializers.py