feat(ui): in read-only author mode, hide track changes in fullwaxeditor

As requested in Mattermost, this hides all track changes functionality in the FullWaxEditor component when readOnly is set to true and authorComments is set to true, so that authors don't see what's been changed, only the results of the changes.

A variation is possible where the track changes functionality wouldn't be visible but additions and deletions in the text would be. If that's what's wanted, just don't use the CSS rules that were added here.