Bug 800402 - [email] UI: Show the number of unread messages in the message-list header after the folder name

We're trying to switch away from the jstut (a thing I created but never meaningfully shipped) scribble-inspired syntax you'll see used throughout and to JSDoc 3-compatible syntax.  Since you have some tabs still in here and I'm going to give some additional details, it probably makes sense to convert.  The JSDoc idiom for this can be found at http://usejsdoc.org/tags-typedef.html