751 Refactor loaders to unify base class (#752)
751 Refactor loaders to unify base class (#752)

* [DLMED] refactor loaders to remove duplicated part

* [MONAI] python code formatting

Co-authored-by: monai-bot <44c1f063c38035faefb6ff7e163cf4202a207288@gmail.com>
Co-authored-by: Eric Kerfoot <8237db260dc636e440d6760cc12eb2b38acb836e@users.noreply.github.com>
Project-MONAI/MONAI,Project-MONAI/MONAI,Project-MONAI/MONAI,Project-MONAI/MONAI