Implement private replies into the quick replies

Behat tests provided.  Prerequisites: A teacher and student enrolled in a course A forum activity within the course. Add a discussion in the activity as a teacher. Instructions: As a student, go to the forum activity and the discussion started. Click on the reply link Confirm you cannot see a "Private reply" checkbox. Enter a message and submit via the quick reply feature As a teacher, go to the forum activity and the discussion created. Reply to the student's post by clicking the 'Reply' link Confirm you can see 'Private Reply' checkbox. Enter a message and submit. Confirm you are navigated to the newly created post and you do not see "This post was made privately and is not visible to all users." Repeat #6 and #7 Check the 'Private Reply' checkbox Enter a message and submit Confirm you are navigated to the newly created post and you do see "This post was made privately and is not visible to all users."