Replaced some classes to functions #37 . Still need to update some tests

bob/learn/tensorflow/loss/BaseLoss.py

bob/learn/tensorflow/loss/ContrastiveLoss.py

bob/learn/tensorflow/loss/TripletAverageLoss.py

bob/learn/tensorflow/loss/TripletFisherLoss.py

bob/learn/tensorflow/loss/TripletLoss.py

bob/learn/tensorflow/loss/__init__.py

bob/learn/tensorflow/network/Chopra.py

bob/learn/tensorflow/network/__init__.py

bob/learn/tensorflow/network/utils.py

bob/learn/tensorflow/script/lfw_db_to_tfrecords.py

bob/learn/tensorflow/script/train.py

bob/learn/tensorflow/test/test_cnn.py

bob/learn/tensorflow/test/test_cnn_other_losses.py

bob/learn/tensorflow/test/test_cnn_scratch.py

bob/learn/tensorflow/trainers/SiameseTrainer.py

bob/learn/tensorflow/trainers/Trainer.py

bob/learn/tensorflow/trainers/TripletTrainer.py