Writes model generated, original and real images to Tensorboard.

def _write_images(self, iteration:int)->None:
        "Writes model generated, original and real images to Tensorboard."
        trainer = self.learn.gan_trainer
        #TODO:  Switching gen_mode temporarily seems a bit hacky here.  Certainly not a good side-effect.  Is there a better way?
        gen_mode = trainer.gen_mode
        try:
            trainer.switch(gen_mode=True)
            self.img_gen_vis.write(learn=self.learn, trn_batch=self.trn_batch, val_batch=self.val_batch, 
                                    iteration=iteration, tbwriter=self.tbwriter)
        finally: trainer.switch(gen_mode=gen_mode)