Allow comments on study documents

Created by: rcelina

it would be nice to have a "comment function" for the study documents, there are two reasons for that... first most summarys have a comment to contact the person who wrote it if any mistakes are found, in addition the writers put their e-mail address. with a comment function it wouldn't be nessecairy for the writers to publish their e-mail address. Second, it would be great to have the comment function especially for exams so if someone needs help with an specific exercise they can get help easily.