GitLab

* use_sigmoid_cls -> cls_sigmoid_loss; use_focal_loss -> cls_focal_loss

* fix flake8 error

* cls_sigmoid_loss - > use_sigmoid_cls

* rename normalize to norm_cfg

* update configs

* Update resnet.py

* support GN in RetinaHead

* add conv_cfg argument for RetinaHead

* add model upgrading tool and update retinanet model urls

* minor fix for regex strings

* add cpp sigmoid focal loss

* modify interface

* format cpp code, support, fix pep8 error

* format cpp code as google style