Add ResNet MCMC baselines from SGMCMC paper

[dustinvtran]

@jereliu @flwenzel. One potential issue is that @flwenzel's SGMCMC paper was on the older Edward2 ResNet-20 baseline script (which itself was loosely based on the UQ benchmark's). This is before we upgraded to WRN-28-10.

@znado Not sure what we want to do with the resnet-20 baselines. We could have a separate directory in the CIFAR baselines for it if we'd like.

[Jordy-VL]

@dustinvtran @znado Is there any concrete plan to make SG-MCMC and SG-HMC implementations in TensorFlow?

I have only found some implementations in Pytorch, but they might help in conversion: https://github.com/reml-lab/URSABench/blob/master/URSABench/inference/sghmc.py

Thanks in advance for the reply!