Refactor UMLListView to use Object_Factory

The createItem, createUMLObject and createChildUMLObject methods are replaced
by calls to Object_Factory. The only changes to Object_Factory involve
pre-setting a name on classifier list items so there's no behavioural change
(item creation in the list view is 'quick' - no dialog popping up).

Related code cleanup:
* unused diagram creation code
* unused itemRenamed method (UMListViewItem handles that)
* unused lines in createChildUMLObject handling renaming of classifier list
items, which was also handled by the UMLListViewItem (e.g. determining the
return type of an operation based on the new text of a list item)