Andrew Lyons authored Mar 19, 2016 and Peter Dias committed Apr 04, 2019

This patch adds new capabilities:
'mod/forum:postprivatereply'   - whether a user is able to post private replies; and
'mod/forum:readprivatereplies' - whether a user is able to read private replies.

Private replies are only visible to the intended recipient (the author of
the parent post), the author of the private reply, and those with the
ability to read private replies.

If a post is private then it cannot be replied to further.