Make selection:listitem a hippo:compound (was: EditmodelWorkflowImpl does not handle selection:listitem correctly)

A compound type created through the type editor with a value list item compound field should have a selection:listitem as child in the cnd definition. This is because a selection:listitem is an nt:base and the type editor will only define the new compound as a hippo:compound and a hippostd:relaxed which do not contain nt:base as a child.