Lights get virtual destructor and correct types

src/light.cc

@@ -18,6 +18,10 @@ Light::Light(const Color& color,
 { }
 
 
+Light::~Light()
+{ }
+
+
 Color&
 Light::GetColor()
 {

src/light.hh

@@ -20,9 +20,11 @@ struct Light
     Light(const basics::Color& color,
           const Double& intensity = 1.0);
 
+    virtual ~Light();
+
     basics::Color& GetColor();
     const basics::Color& GetColor() const;
-    void SetColor(basics::Color& color);
+    void SetColor(const basics::Color& color);
 
     Double GetIntensity() const;
     void SetIntensity(const Double& intensity);