Closes #3379

• Attributes which are removed will automatically go to the object's api_kwargs.
• Attributes which are new to the class won't be available in the unpickled version

Checklist for PRs

• Added .. versionadded:: version, .. versionchanged:: version or .. deprecated:: version to the docstrings for user facing changes (for methods/class descriptions, arguments and attributes)
• Created new or adapted existing unit tests
• Documented code changes according to the CSI standard
• Added myself alphabetically to AUTHORS.rst (optional)
• Added new classes & modules to the docs and all suitable __all__ s