Create placeholder django apps for credentials

cms/envs/common.py

lms/envs/common.py

openedx/core/djangoapps/credentials/__init__.py

openedx/core/djangoapps/credentials/api/__init__.py

openedx/core/djangoapps/credentials/api/urls.py

openedx/core/djangoapps/credentials/api/v1/__init__.py

openedx/core/djangoapps/credentials/api/v1/tests/__init__.py

openedx/core/djangoapps/credentials/api/v1/views.py

openedx/core/djangoapps/credentials/models.py

openedx/core/djangoapps/credentials/tasks.py

openedx/core/djangoapps/credentials/tests/__init__.py

openedx/core/djangoapps/credentials/urls.py