Replace for-loop with std::transform() for deep copy.
Remove one-time-use nNodes.
Replace for loop with std::for_each.
Add getTrianglesPointId() and getTrianglesPoint() in Surface.

This clarifies usage in a lot of places.
Generalize getPlaneCoefficients() to three input points.

Was implemented only to accept triangles.
Replace Surface::operator[] return value.

This is required for further refactoring which will remove vector of triangles.
Store only point indices of triangles in Surface.