Link Comments to Workshop booking instances

[ankitjavalkar]

• A user (instructor or coordinator) should be able to make comments on workshops
• Coordinators can only comments on workshops that they themselves have proposed
• Instructors should be allowed to hide comments so that it is visible only to other instructors and not to coordinators
• Coordinator comments will always be publicly visible to the coordinator commentor and to the instructors
• Record the creator of the comment and the timestamp of creation