[WFLY-266] Notification Support

* add notifications to AS7 resources description
  * notifications are described in :read-resource-description operation
    if the notifications boolean is true
  * all resources emit 3 types of notifications by default:
    - resource-added
    - resource-removed
    - attribute-value-written
* NotificationDefinition let any resources describe the notifications
  they can emit by registering them in the ManagementResourceRegistration
* add NotificationSupport to let AS7 resource register/unregister
  notification handlers and emit notifications
* emit notification for resource added/removed and attribute-value-written
  directly from the AbstractOperationContext.
* emit notifications for server lifecycle notifications (server-started,
  server-stopped, server-restarted, server-killed & server-destroyed)

Notification emitted by OperationContext.emit(Notification) are
effectively sent at the end of the operation execution if it is
successful. This ensure that the order of notifications emitted by a
single OperationContext will be received in the same order (unless
they are emitted during the ResultHandler execution).