Disambiguate class name vs object name; rename InterferenceFunction -> Interference

• Remove the dynamic setting of names.
• Resolve the long-standing ambiguity of class name vs object name.
• INode now has a virtual function className; final children also have static member class_name.
• To resolve an inconsistency between GUI and core, rename InterferenceFunction -> Interference.
• Provide MultiLayer::setSampleName, yet unsupported in the GUI.

GUI/Views/SampleDesigner/ConnectableView.cpp

@@ -25,7 +25,6 @@
 
 ConnectableView::ConnectableView(QGraphicsItem* parent, QRectF rect)
     : IView(parent)
-    , m_name("Unnamed")
     , m_color(Qt::gray)
     , m_rect(rect)
     , m_roundpar(0)