Implemented API for model node creation.

hello_cube smoke test now adds a model node and assigns the built-in cube model

kraken/nodes/KRCollider.h

@@ -70,7 +70,7 @@ public:
   float getAudioOcclusion();
   void setAudioOcclusion(float audio_occlusion);
 
-  void render(RenderInfo& ri);
+  void render(RenderInfo& ri) override;
 
 private:
   KRMesh* m_model;