[models] Move repeated functions into specialized models

src/mednet/libs/classification/models/alexnet.py

...mednet/libs/classification/models/classification_model.py

src/mednet/libs/classification/models/densenet.py

src/mednet/libs/classification/models/pasa.py

src/mednet/libs/segmentation/models/driu.py

src/mednet/libs/segmentation/models/driu_bn.py

src/mednet/libs/segmentation/models/driu_od.py

src/mednet/libs/segmentation/models/driu_pix.py

src/mednet/libs/segmentation/models/hed.py

src/mednet/libs/segmentation/models/lwnet.py

src/mednet/libs/segmentation/models/m2unet.py

src/mednet/libs/segmentation/models/segmentation_model.py