code: function findRegisteredIdentifier(modelOrCollection) {
  	var foundKey;
  
  	for(var key in this.registeredModelsAndCollections) {
  		var registeredModelOrCollection =
  			this.registeredModelsAndCollections[key];
  
  		if(modelOrCollection.constructor === registeredModelOrCollection) {
  			foundKey = key;
  			break;
  		} else {
  			if(_.has(registeredModelOrCollection, 'collectionClass') &&
  				modelOrCollection.constructor ===
  				registeredModelOrCollection.collectionClass) {
  
  				foundKey = key;
  				break;
  			}
  		}
  	}
  
  	return foundKey;
  }
docs: Function: findRegisteredIdentifier
  Scans the registered models and collections for the given model. When found,
  the identifier of the registration gets returned. Otherwise undefined is
  returned.
  
  Parameters:
  (<Barefoot.Model>, <Barefoot.Collection>) model - Concrete instance of a
  model or collection.
  
  Returns:
  (String, undefined) the identifier of model if found, undefined if no
  match