ADD/SAVE PHOTO TAPPED
//create a new item in CD, save to CD, pop back to VC
//get context
if let context = (UIApplication.shared.delegate as? AppDelegate)?.persistentContainer.viewContext {
let photoToBeSaved = Photo(entity: Photo.entity, insertInto: context)
photoToBeSaved.imageCaption = textFieldData.text!
//image is save as DATA not a UIImage, so we have to do a conversion here to change data types: