* [example] added code for training speech command dataset
* update kes_model.py
* update kes_model.py
* format
* format
* add more comments to explain the new classifier designed for speech command classification task
* add copyrigh info
* update copyrigh info of classifier.py
* modifying some implmentations of mdtc to get the model torch-scripting through
* modifications to get the mdtc model torch-scriptable
Co-authored-by: lxiao336 <shawl336@163.com>