Add C++ nested class example

This also reverts the nested class additions to the Java/C# 'class' example
so that the 'class' example remains identical across different language modules

Examples/csharp/nested/example.i

@@ -0,0 +1,13 @@
+%module example
+
+// This example shows how wrappers for numerous aspects of C++ nested classes work:
+// Nested static and instance variables and methods and nested enums
+
+%include <std_string.i>
+
+%{
+#include "example.h"
+%}
+
+%include "example.h"
+