Metro notifications

Introduce Metro notifications (Win 8 only).  Note that to display a metro notifications, you need to have a link installed on the start menu.  This will install an invisible link when the `debugInstall` configuration value is `true`.
Actually I thought about generating the content from `Event`, but I realized that if you were willing to introduce links or typographical enrichments in the notifications, you may need the pieces of information, rather than the dumped string. Or was I completely wrong?