Added asString-method, created default constructor to be used by Google Datastore and replaced PhotoId by a string
Added asString-method, created default constructor to be used by Google Datastore and replaced PhotoId by a string

tfrdidi/MigrateWahlzeitIntoTheCloud,tfrdidi/MigrateWahlzeitIntoTheCloud,tfrdidi/MigrateWahlzeitIntoTheCloud