* Add a TreeViewer that constructs a DynamicTreeViewer whose UI provider
  uses the methods and kernel services for IHierarchicElements and
  NamedElements.
* The Viewer uses a composition principle where a client must provide
  TreeView (JavaFX), a root element (AF3), and a content provider that
  selects the elements to be displayed.
* Add two basic content providers that a) list all children below the
  given root element and b) list all children of a given type.

Issue-Ref: 3209
Issue-Url: https://af3-developer.fortiss.org/issues/3209


Signed-off-by: Alexander Diewald <diewald@fortiss.org>