The "overview" and "about_sidebar_html" fields in the
CoursewareInformation view (/api/courseware/course/{courseId}) were
returning unsanitized HTML and relying on the client to sanitize it.
This commit shifts that work to the server side (clean_dangerous_html)
to remove potentially dangerous tags when generating the response. The
source of this data is modified in the "Settings and Details" section
of a course in Studio.
53c25b9cd8