Added create_model.py to allow creation of model folder

[babaraza]

This file automates the model folder and file copying required after user fine-tunes the model using their own custom dataset.

Usage:
python create_model.py -create mymodel -model 124M -run run2

This will:

• Create a folder inside models called mymodel
• Copy encoder.json, hparams.json, vocab.bpe to mymodel from 124M folder
• Copy checkpoint, model-xxx.data, model-xx.index, model-xx.meta to mymodel from run2

Now a user can simply generate samples using their own model:
python interactive_conditional_samples.py --model_name mymodel