Add a NotificationHandler interface

That way, the app developer can decide what to do with the notification.
 By default, ' DefaultDialogNotificationHandler` will be used, which displays an alert dialog whose Ok button opens the rich media url if present.
Rename method to MalcomLib.checkNotificaction

Also improve a couple of javadocs
Merge pull request #19 from MyMalcom/notification-handler

Notification handler