Expand the contentPostedIn() method to include reviews

As per title, right now the function \IPS\Node\Model::contentPostedIn() works only if the class has a $commentClass value defined. If you have an application that only has reviews and not comments the method does nothing. The review of an Item is something a user has posted too, not just a comment.

For now I have added a new method in my own Item class that works in a similar way, using the $reviewClass variable of course.