[WIP] Add Swin Transformer (#511)

* add Swin Transformer

* add Swin Transformer

* fixed import

* Add some swin training settings.

* Fix some filename error.

* Fix attribute name: pretrain -> pretrained

* Upload mmcls implementation of swin transformer.

* Refactor Swin Transformer to follow mmcls style.

* Refactor init_weigths of swin_transformer.py

* Fix lint

* Match inference precision

* Add some comments

* Add swin_convert to load official style ckpt

* Remove arg: auto_pad

* 1. Complete comments for each block;

2. Correct weight convert function;

3. Fix the pad of Patch Merging;

* Clean function args.

* Fix vit unit test.

* 1. Add swin transformer unit tests;

2. Fix some pad bug;

3. Modify config to adapt new swin implementation;

* Modify config arg

* Update readme.md of swin

* Fix config arg error and Add some swin benchmark msg.

* Add MeM and ms test content for readme.md of swin transformer.

* Fix doc string of swin module

* 1. Register swin transformer to model list;

2. Modify pth url which keep meta attribute;

* Update swin.py

* Merge config settings.

* Modify config style.

* Update README.md

Add ViT link

* Modify main readme.md

Co-authored-by: Jiarui XU <xvjiarui0826@gmail.com>
Co-authored-by: sennnnn <201730271412@mail.scut.edu.cn>
Co-authored-by: Junjun2016 <hejunjun@sjtu.edu.cn>