Entity now can be linked to a mesh.

Only support cube generated from code no light no nothing

Game/Entity/Entity.h

@@ -23,6 +23,7 @@ struct Entity final
     const Juliet::Class* Kind;
     DerivedType          Derived;
     float                X, Y;
+    index_t              MeshInstance = indexMax;
 };
 
 template <typename EntityType>