Moved Model::EnableDraw to SceneNode::EnableDrawing

Same goes for Model::IsDrawEnabled() => SceneNode::IsDrawingEnabled()
Is Drawable is now a pure virtual method from SceneNode


Former-commit-id: 217c6a21a98206ee0b283aaa216d419696a70faf

src/Nazara/Graphics/SceneRoot.cpp

@@ -31,6 +31,11 @@ nzSceneNodeType NzSceneRoot::GetSceneNodeType() const
 	return nzSceneNodeType_Root;
 }
 
+bool NzSceneRoot::IsDrawable() const
+{
+	return true;
+}
+
 bool NzSceneRoot::FrustumCull(const NzFrustumf& frustum)
 {
 	NazaraUnused(frustum);