Put "type" attribute in base composite type

[S-Gaertner]

5.2.9/5.6.8: The type attribute should be put in the base composite type malxml:Composite, not in each derived type. The latter is especially difficult, because the attribute should be put in the malxml namespace, but composites are generally defined in a completely different namespace. One "drawback" could be that then also lists need to have a malxml:type attribute. On the other hand, this makes sense because lists by definition can only contain elements of the same concrete type.