Fix Certificates import and signals code

cms/envs/common.py

common/djangoapps/entitlements/models.py

common/djangoapps/entitlements/tests/test_models.py

...on/djangoapps/pipeline_mako/templates/static_content.html

common/djangoapps/student/models.py

common/djangoapps/student/tests/test_certificates.py

common/djangoapps/student/tests/test_refunds.py

common/djangoapps/student/tests/test_views.py

common/djangoapps/student/tests/tests.py

common/djangoapps/student/views.py

lms/djangoapps/badges/events/course_meta.py

lms/djangoapps/badges/events/tests/test_course_meta.py

...goapps/badges/migrations/0002_data__migrate_assertions.py

lms/djangoapps/badges/tests/test_models.py

lms/djangoapps/certificates/admin.py

lms/djangoapps/certificates/api.py

lms/djangoapps/certificates/apis/v0/tests/test_views.py

lms/djangoapps/certificates/apps.py

...goapps/certificates/management/commands/cert_whitelist.py

...apps/certificates/management/commands/create_fake_cert.py