[WFLY-3603] Add Global Resource Notifications

* add global notifications for resources:
  * resource-added when a resource is added to the management model
  * resource-removed when a resource is removed from the management
    model
  * attribute-value-written for resources that allow to write
    attributes when an attribute value is successfully changed.
    This notification contains a data set composed of:
    * name - the name of the attribute that has been changed
    * old-value - the value of the attribute before it was changed
    * new-value - the value of the attribute after it was changed

The old-value and new-value are *not* resolved (an attribute that is
undefined and has a default value will return "undefined" as its
old-value).

JIRA: https://issues.jboss.org/browse/WFLY-3603
Merge pull request #45 from jmesnil/WFLY-3603_global_resource_notifications

[WFLY-3603] Add Global Resource Notifications