ChG

Results 3 issues of ChG

For issue #820 Datalab now can accept an existing Datalab instance and use its statistics information for finding issues for new data. This only support label issue and `pred_probs` only....

fixes #1053 just increase the number of samples of the rare class, but it is still a relatively small number.

fixes #241 The requirement for `transformers` doesn't match in `install.md` and `install_CN.md`. The wrong version in `install_CN.md` will cause an error.