Implementation of training various models with knowledge distillation.

• Run jupyter notebooks located in dataprepare

1. All models should be placed at ./models. They could be either separated py file or module directory, but they should be defined at ./models/__init__.py so that other program can call them without indicating their subdirectories.

2. Two Dataloader mode exists and those can be switched by argument
   Extracting outputs from cumbersome model (1) on the fly, (2) on the memory\ So all cumbersome models should have method extract which can gets various arguments.
   extract_and_save.py call extract method from cumbersome pretrained model and save them.

3. Model's initializing arguments should be defined at yaml config file. Same configuration file can be used at both extract_and_save.py and main.py

4. Distillation use one model which contains both cumbersome and small model.
   Their parameters, pretrained path and all other options for initializing each of models are supplied by a yaml file.
   Those are implemented in ./models/kd.py