Add video transcript config model flags - EDUCATOR-1224

cms/djangoapps/contentstore/views/tests/test_videos.py

cms/djangoapps/contentstore/views/videos.py

cms/static/js/factories/videos_index.js

cms/static/js/spec/views/active_video_upload_list_spec.js

cms/static/js/views/active_video_upload_list.js

cms/static/js/views/course_video_settings.js

cms/templates/js/course-video-settings.underscore

cms/templates/videos_index.html

openedx/core/djangoapps/video_config/admin.py

openedx/core/djangoapps/video_config/forms.py

...evideotranscriptenabledflag_videotranscriptenabledflag.py

openedx/core/djangoapps/video_config/models.py

openedx/core/djangoapps/video_config/tests/test_models.py