Sagemaker p27 notebooks

[ffeijoo]

Changelog:

• Notebooks running kernel conda_tensorflow_p27 (fixed DenseNet3D import)
• Data preparation included in notebooks
• Notebook for training, deploying and serving the inference endpoint in Sagemaker (sagemaker_train_external)
• Notebook for training locally, exporting the model and: (a) importing and serving the inference endpoint in Sagemaker, or (b) running predictions locally (sagemaker_train_local)
• A few minor bug fixes: (a) prevent calculating losses if running in PREDICT mode, and (b) call the _predict_result with model instead of model.logits