Register and enable some FolksDummy.PersonaStores.
For each of the persona stores in stores, register it with this backend. If enable_stores is true,
            added stores will also be enabled, emitting Folks.Backend.persona_store_added for each newly-enabled store. 
            After all addition signals are emitted, a change notification for Folks.Backend.persona_stores will
            be emitted (but only if at least one addition signal is emitted).
Persona stores are identified by their Folks.PersonaStore.id; if a store in stores has the 
            same ID as a store previously registered through this method, the duplicate will be ignored (so 
              Folks.Backend.persona_store_added won't be emitted for that store).
Persona stores must be instances of FolksDummy.PersonaStore or subclasses of it, allowing for different persona store implementations to be tested.
| stores | set of persona stores to register | 
| enable_stores | whether to automatically enable the stores | 
0.9.7