Forum: Implement a "Private Reply" option

Test on any device. Login to a 3.7 site as a student. Go to a forum and add a new discussion. Login to the same site as a teacher. Go to the created forum discussion created as a student. Click "Reply" and check  the"Reply privately" checkbox displayed below the editor. Write some message and click "Post to forum". Check that the new post contains the text "The post was made privately and is not visible to all users" and it does not have a "Reply" button. Send another reply but do not check "Reply privately" this time. Switch the device to offline. Send a reply again checking "Reply privately". Check that the post is saved offline and it contains the text "The post was made privately and is not visible to all users". Click the "Edit" button in the reply and check that the edit form contains ""Reply privately" checkbox and it is checked. Close the form (save or cancel) and switch to online. Sync the discussion (with a pull to refresh). Check that the offline post is saved online as a private reply. Delete the site from the app and login again to the site as a teacher. Go to the course of the forum. Enable "Show download options" and download the forum. Switch the device to offline. Check that you can reply to a post and the post is saved. Login to the same site as the student. Go to the forum discussion. Check that the private replies (sent by the teacher) contains the text "The post was made privately and is not visible to all users" and it does not have a "Reply" button. Click the "Reply" button in the public post. Check that the form does not contain the "Reply privately" checkbox. Login to the same site as another student (not the same used in step 1). Go to the forum discussion. Check that the private replies created previously are not displayed. Login to a 3.6 site as a teacher. Go to a forum with some posts. Click the "Reply" button in the public post. Check that the form does not contain the "Reply privately" checkbox. Send the post and check that it is saved without errors.