/*!
* Initialization of DATASource.
* \param collectionView The used UICollectionView.
* \param fetchRequest The used NSFetchedResultsController.
* \param cellIdentifier The used cell identifier.
* \param mainContext A NSManagedObjectContext in the main thread.
* \param configure A block to configure the cell.
* \returns An instance of DATASource.
*/
- (instancetype)initWithCollectionView:(UICollectionView *)collectionView
fetchRequest:(NSFetchRequest *)fetchRequest
cellIdentifier:(NSString *)cellIdentifier
mainContext:(NSManagedObjectContext *)mainContext
configure:(DATAConfigureCell)configure;