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.