Add ATNs for ImageNet dataset

[gchhablani]

This issue is a continuation of #19. The code for MNIST will be merged in #85. The original paper also mentions architectures for ImageNet models. It would be nice to have these implementations in the repository.

In this comment, I have added dummy code for all architectures needed. However, the implementation should contain exactly the same number of channels/kernel sizes as the original model.

This will need effort in checking the what input/output paddings and strides will work given the architecture.

[soham-chitnis10]

I would like to take this up