Classes/Courses enhancements

[AlexTr]

• [ ] block in a group with all answers by students which are pending approval (with option to show all answers) which is visible to admins, moderators only
• [ ] class setting - allow multiple root comments for students
• [ ] comments modifications: additional control (when comments approving is enabled) which shows status of comment for student - approved or not and control to approve or reject for admin/moderator
• [ ] notifications: send notification to student when his answer is approved or rejected

Extend groups/spaces/events/etc

• [ ] allow to filter members by roles in members list
• [ ] allow to choose group roles in "Who can post" privacy field
• [ ] allow to set access to chat/messenger by roles
• [ ] (optional) search inside the group
• [ ] (optional) ability to add pages to a group

Related old issue - #1904