Use pythonic sequence ducktyping instead of hardcoding to list type

[Bartvds]

The list of objects,and the update_fields and exclude_fields arguments break when passed a set, tuple, iterable or any other sequence type that is not specifically a list.

This is not very pythonic, most API's allow to pass whatever and will convert if their internals require a specific type of sequence.

This is annoying if we pass things like dict.keys() as update_fields, or a set of deduped objects etc.