Tfkeras transition

1. Added Migrate script to convert tf1 models to tf.keras models
2. Added script to generate an mask image mapping
3. Added several network structures (mobile_net, rest_net, original u_net)
4. Added tensorboard integration to display training progress while training
5. Refactored most of backend code for tf.keras integration
6. Added several metrics

merged

mentioned in commit 29210725