* add new load dygraph func

* update load_pretrain_params

* update load_dygrah_params

* Update save_load.py

* Update train.py

* Update save_load.py

* return {} when path is None

* return {} when path is None

Fixed variable name

Co-authored-by: Nlittletomatodonkey <2120160898@bit.edu.cn>

add a necessary check for checkpoints, if you miss the file prefix and it will not execute the checkpoints codes

remove the  useless parameters  and  update import