[SofaPython3/Plugin] Add GetCustomClassName to Prefab (#288)

So the string returned is now "Prefab" instead of "Node".

Author: damienmarchal

Plugin/src/SofaPython3/Prefab.h

@@ -59,6 +59,8 @@ class SOFAPYTHON3_API Prefab : public BasePrefab
     void reinit();
     virtual void doReInit() ;
 
+    static const std::string GetCustomClassName(){ return "Prefab"; }
+
     void addPrefabParameter(const std::string& name, const std::string& help, const std::string& type, pybind11::object defaultValue = pybind11::none());
     void setSourceTracking(const std::string& filename);
     void breakPrefab();