Update Benchmark Results, New Features, and Documents in V0.2.6

[Lupin1998]

Updateing new features:

1. Update new backbone architectures (MogaNet, and provide config files and README.md. Fix the distillation head in DeiT.
2. Support SeeSaw loss for long-tail classification tasks.

Uploading Benchmark Results (release):

1. In a2mim-in1k-weights, we release weights and logs of self-supervised learning methods with end-to-end fine-tuning protocols on ImageNet based on ResNet-50 and ViT-Base architectures.

Updating documents:

1. Update documents of the new backbone and self-supervised methods.
2. Update self-supervised learning Model_Zoo_selfsup.md and awesome paper lists.

[Lupin1998]

Update benchmark results, new features, and documents for OpenMixup V0.2.6 (issue #31).