[Discussions] Notify all students using @all in forums

[LParker21]

Problem statement:

You can only tag one user at a time in discussion forums using the @ function.

Proposed solution:

Add the @All function to notify all students in the discussion forum (if split by groups, only the students assigned to the proximal forum would be notified, not all students in the course) of a written reply.

User role(s):

instructor,student