Train with a different backbone (Resnet-50 or ResNet-18)

[alphjheon]

@YuwenXiong @ancientmooner @daijifeng001 @einsiedler0408 @HaozhiQi: Is it possible to run the training experiments, with a different backbone? Have you implemented such an experiment for an ablation study? Any help provided for running such an experiment would be highly appreciated.