* Code for paper "Dynamic R-CNN: Towards High Quality Object Detection via Dynamic Training"

* update configs/dynamic_rcnn/dynamic_rcnn_r50_fpn_1x.py

* reformat code

* simplify code

* update model link

* simplify code

* simplify code logic

* simplify code and add comments

* minor updates of the docstring

Co-authored-by: Jiarui XU <xvjiarui0826@gmail.com>
Co-authored-by: Kai Chen <chenkaidev@gmail.com>