Place on bed improvements

- works with large meshes
- area discrimination takes into account scaling of the object
- planes are recalculated when some volume's type is changed (e.g. from a part to modifier mesh)

src/slic3r/GUI/GLGizmo.hpp

@@ -403,6 +403,8 @@ private:
 
     // This holds information to decide whether recalculation is necessary:
     std::vector<Transform3d> m_volumes_matrices;
+    std::vector<ModelVolume::Type> m_volumes_types;
+    Vec3d m_first_instance_scale;
 
     std::vector<PlaneData> m_planes;
     mutable Vec3d m_starting_center;