fix: added list_files method back, matching docs

[sg-s]

changes

• [x] closed https://github.com/deeporiginbio/deeporigin-client/issues/80
• [x] updated docs to point users to .api, not _api
• [x] Use platform API to show human names in dataframe header
• [x] write tests for dataframe.to_deeporigin (to be run against a live instance)
• [x] fix a bug where writing a column with missing values is not possible
• [x] if nothing is edited, use the created by field in the dataframe header
• [x] update documentation about new functions to delete workspaces
• [x] update documentation about new functions to delete databases
• [x] refactored tests to use a common config block for pytest
• [x] updates to CLI to support deleting databases using new endpoints
• [x] updates to CLI to support deleting workspaces using new endpoints
• [x] updates to CLI to support deleting rows using new endpoints

screenshots