Updated the configuration classes to load local tokenizer of teacher, emulator and student.

[youralmight]

Researchers usually download the huggingface transformers model to local storage to avoid errors when they don't have a stable network connection. When using training or inference script, SSL error or timeout errors sometimes occurs even if the parameter --model is set to the path of the downloaded model, because the code is trying to load the tokenizer from huggingface.

To avoid such errors, I added an 'if' branch to the __init__ functions of the configuration classes.