Fix global unread message counting

Fixed the global counting of unread messages. This makes the "unreadCount"
variable in storage to stay in sync with the sum of unread messages in each
conversation. To achieve this, the controller_view updates the global
variable whenever messages are received or read.

js/background.js

@@ -172,8 +172,6 @@
             type           : 'incoming'
         });
 
-        var newUnreadCount = storage.get("unreadCount", 0) + 1;
-        storage.put("unreadCount", newUnreadCount);
         extension.navigator.setBadgeText(newUnreadCount);
 
         return message;

js/conversation_controller.js

@@ -29,11 +29,10 @@
         },
         updateUnreadCount: function(model, count) {
             var prev = model.previous('unreadCount') || 0;
-            if (count < prev) { // decreased
-                var newUnreadCount = storage.get("unreadCount", 0) - (prev - count);
-                setUnreadCount(newUnreadCount);
-                storage.put("unreadCount", newUnreadCount);
-            }
+            var newUnreadCount = storage.get("unreadCount", 0) - (prev - count);
+            setUnreadCount(newUnreadCount);
+            storage.remove("unreadCount");
+            storage.put("unreadCount", newUnreadCount);
         }
     }))();