Support swin transformer

[ZwwWayne]

This PR adds Swin Transformer as an example to show how we can use MIM to run Swin Transformer for object detection and segmentation with only two python file and several configs.

[kennymckormick]

Besides, we want to keep the examples as simple as possible. Can we remove all those base configs and merge them into the configs actually used? So that we will have much fewer files in this example.

[kennymckormick]

@ZwwWayne Do you have some time to push this PR forward. I think it can be merged after some reorg (to reduce file numbers) and adding a requirements.txt. I think this PR will be a milestone of MIM-Examples.

[ZwwWayne]

@ZwwWayne Do you have some time to push this PR forward. I think it can be merged after some reorg (to reduce file numbers) and adding a requirements.txt. I think this PR will be a milestone of MIM-Examples.

sure, will make it by this week

[ZwwWayne]

@kennymckormick Can have a look. Now, this PR works with MMDetection. I cannot run mmseg due to some reasons in mim. Will check that tomorrow.

[kennymckormick]

Hi, @ZwwWayne , will you support Swin + segmentation in this PR (I think detection only is OK)? Besides, would you please also provide a Swin checkpoint so that users can run testing in this MIM example.