Add proper support for ResNet

[t-rad679]

There's an enum containing info to support several different models, but none of the non-VGG models are ready for use without additional knowledge. Specifically, it is as yet unclear which layers should be selected for style and which for content--I was not able to determine how the creators decided on VGG layers in the tutorial. In addition to supporting these additional models, it would be great to more generally understand why certain layers would be selected over others.

This ticket is for ResNet.