Use nsIMsgFolderListener for some notifications

Change to use nsIMsgFolderListener for add/remove notifications.
This way we don't get OnItemAdded/OnItemRemoved spam when moving
a bunch of messages between folders. In the nsIMsgFolderListener
parlance, that would trigger a msgsMoveCopyCompleted instead; we
can just ignore that, because that won't change the net total of
unread messages.

Also in msgAdded/msgsDeleted handlers, check to see that the msg
in question is unread. If it isn't, then that won't change total
unread count either.
Merge branch 'master' of github.com:bstreiff/unread-badge
Remove Timer.jsm reference.

I had added this in a prior change for code I ultimately did not use.
Remove the import(), since it is no longer necessary.
Formatting changes.

Make a pass with a formatting tool to fix up indents and brace positions.

I prefer brace-on-new-line but automatic semicolon insertion makes it more
difficult to do. Thanks, Javascript!