Emitted when one or more Personas are added to or removed from the store.
This will not be emitted until after PersonaStore.prepare has been called.
| added | a set of Personas which have been removed | 
| removed | a set of Personas which have been removed | 
| message | a string message from the backend, if any | 
| actor | the Persona who made the change, if known | 
| reason | the reason for the change | 
0.5.1