Streamlined normalization setup/reload from checkpoint on models

helpers/generate_histograms.py

src/mednet/engine/trainer.py

src/mednet/models/classify/alexnet.py

src/mednet/models/classify/densenet.py

src/mednet/models/detect/faster_rcnn.py

src/mednet/models/model.py

src/mednet/models/segment/driu.py

src/mednet/models/segment/driu_bn.py

src/mednet/models/segment/driu_od.py

src/mednet/models/segment/driu_pix.py

src/mednet/models/segment/hed.py

src/mednet/models/segment/lwnet.py

src/mednet/models/segment/m2unet.py

src/mednet/models/segment/unet.py

src/mednet/scripts/train.py

tests/classify/test_cli.py

tests/segment/test_cli.py