Exported method parameters need to support dict types

There is no dict marshaller. Therefore, although it is possible to declare that exported method parameters can be of type dict, it does not work in practice.

eg

    @export_write_operation()
    @operation_parameters(
        dict_param=Dict(
            key_type=xxxxxx,
            value_type=yyyyyy))
    @operation_for_version('devel')
    def someMethod(dict_param):