Interesting and useful. However, the term is ambiguous, since WhatsApp chats are called Groups (Group Chat), the same as Miranda contact Groups. I would rename it to "Default contact group".
By the way, something is creating a new contact group named "Chat rooms" in root group category. Everytime I delete it, it recreates upon restart.
Still new unread messages show up with the same time (the time I open the window for 1st time).
And something new: the status bar shows the name of another chat group!