Fix access to the interator and display a better plot

[adam-narozniak]

It fixes access to the trainloader required to display a batch of CIFAR10 images.
Before:

images, labels = iter(trainloaders[0]).next()

Gives: AttributeError: '_SingleProcessDataLoaderIter' object has no attribute 'next'

Now:

images, labels = next(iter(trainloaders[0]))

Additionally, it creates a more appealing plot of images (bigger plot, space between images, labels directly above the images).
Before (with the iterator access fix):

After:

[danieljanes]

Lgtm!