* [Enhance] New-style CPU training and inference.

* assert mmcv version

* SyncBN to BN in training and testing

* SyncBN to BN in training and testing

* upload untracked files to this branch

* delete gpu_ids

* fix bugs

* assert args.gpu_id in train.py

* use cfg.gpu_ids = [args.gpu_id]

* use cfg.gpu_ids = [args.gpu_id]

* fix typo

* fix typo

* fix typos