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

Er, let's amend that: "The human-readable name of the folder with all utf-7 decoding/etc. performed.  This is intended to be shown to the user, the path should not be.  Folder names should be considered private/personal data and if logged should be marked to be sanitized unless the user has explicitly enabled super-verbose privacy-entraining logs."