* [Feature] Support file_client in dataset initialization

* docstring

* revise osp.exist

* support iSAID aerial dataset

* Update and rename docs/dataset_prepare.md to 博士/dataset_prepare.md

* Update dataset_prepare.md

* fix typo

* fix typo

* fix typo

* remove imgviz

* fix wrong order in annotation name

* upload models&logs

* upload models&logs

* add load_annotations

* fix unittest coverage

* fix unittest coverage

* fix correct crop size in config

* fix iSAID unit test

* fix iSAID unit test

* fix typos

* fix wrong crop size in readme

* use smaller figure as test data

* add smaller dataset in test data

* add blank in docs

* use 0 bytes pseudo data

* add footnote and comments for crop size

* change iSAID to isaid and add default value in it

* change iSAID to isaid in _base_

Co-authored-by: MengzhangLI <mcmong@pku.edu.cn>