Ability to hide courses#168

Issue: Related courses are shown, but we may have courses hosted in different niches which we don’t want shown.

Current workaround: select that course is not shown in catalgo

Current issue: prospective buyers needs to be directed to log in and then to select course

Proposed solution: If we could:
1) mark a course as secret, and the url would not show on catalog but would be accessible via a link that you share
2) have the ability to turn on or off the related course feature (perhaps via tags. Eg if the course is tagged business and related is on - only business courses with that tag will be shown)