SceneGraph: move Implementation::Transformation declaration to SceneGraph.h.

Previously it caused compilation failure when only Object.h was included.

src/SceneGraph/AbstractTransformation.h

@@ -130,11 +130,6 @@ typedef AbstractBasicTransformation3D<Float> AbstractTransformation3D;
 typedef AbstractTransformation<3, Float> AbstractTransformation3D;
 #endif
 
-namespace Implementation {
-    /* See DualQuaternionTransformation.h for example implementation */
-    template<class T> struct Transformation;
-}
-
 }}
 
 #endif

src/SceneGraph/SceneGraph.h

@@ -202,6 +202,10 @@ typedef TranslationTransformation<2, Float> TranslationTransformation2D;
 typedef TranslationTransformation<3, Float> TranslationTransformation3D;
 #endif
 
+namespace Implementation {
+    template<class> struct Transformation;
+}
+
 }}
 
 #endif