NotificationDaemon-based notifications have markup in the banner/body,
but Telepathy-based notifications don't. (Eg, an XMPP message
containing "<b>foo</b>" should show up angle brackets and all, not as
bold.) Fix MessageTray.Notification to allow explicitly specifying
where there should and shouldn't be markup, and use that
appropriately.
https://bugzilla.gnome.org/show_bug.cgi?id=610219