API view to delete course content

[payamnj]

API view to delete course content
Authorization should validate if the user is the platform admin or editor for the organization that the course content is belonged to or a django super user.

request method DELETE
DELETE courses/<course_id>/contents/<content_id>

Should also validate if the content_id sent in the url belonged to the course_id in the url.

should only delete the content if the course is disabled and throw error if the course is enabled.