Create_sub_element method should allow returning the whole element information

The CreateElement endpoint has an additional parameter slim_output that speeds up the creation process. When enabled, only the id of the created element is returned. This is not used by the create_sub_element method. However, only the new element's id is returned. This means that if we later need some additional information about the element (or call any other endpoint method with this element), we need to call RetrieveElement or rebuild an Element instance.

This could be solved by adding an optional parameter that does the same as slim_output.