Prepare the PersonaStore for use.
See Folks.PersonaStore.prepare.
| Folks.PersonaStoreError.STORE_OFFLINE | if the store is offline | 
| Folks.PersonaStoreError.PERMISSION_DENIED | if permission was denied to open the store | 
| Folks.PersonaStoreError.INVALID_ARGUMENT | if any other error occurred in the store | 
0.9.7