Unfurl notifications

Since we no longer have support for list-style notifications, stop
coalescing notifications into batches and just show contents of the last
message received. Also open the window when clicking on a notification
if it has previously been closed.

// FREEBIE

js/background.js

@@ -98,6 +98,7 @@
         });
 
         Whisper.Notifications.on('click', function(conversation) {
+            showWindow();
             if (conversation) {
                 appView.openConversation(conversation);
             } else {