Added identifier in the handler map in onSave event.

As of today, entity id/identifier is available in audit only when a domain class is `auditable` and audit is logged in `AuditEventLog` table. For `handlersOnly` configuration of audit, the handler map for `onSave` event does not contain the identifier.

Since `onSave` event is call as a `PostInsertEvent`, `id` is available at this point of time which can also be made available to handler map. Same can be made applicable for `onChange` event. 

[**JIRA**](http://jira.grails.org/browse/GPAUDITLOGGING-62)