Webhook messaging listener can't access the timestamp field

[alex-lx]

when implementing com.restfb.webhook.WebhookMessagingListener#message, there's no way to access the com.restfb.types.webhook.messaging.MessagingItem#timestamp.

[nbartels]

We modified the listener to have the method duplicated with an additional timestamp parameter. The old methods are marked deprecated. For now we added all the new methods to our abstract class. And so it should be possible very easily to migrate to the new methods.

In the next version we go with this method duplication and remove it in the later releases. So everyone has the possibility to adapt the code before the old methods are removed.