* solov2 init
* solov2 r18 lightweight
* add model docstrings and reformat the code
* add docstrings to model method
* add solov2 big model config and correct some errors in the docstring
* fix linting issues
* refactor code and configs
* rename variables according to the convention
* add and enhance solov2 logic
* add doc strings
* update solov2 config files
* fix norm_cfg in mask head
* minor fix
* update configs
Co-authored-by: BIGWangYuDong <yudongwang@tju.edu.cn>
zhanggefan