ENH: change UnsortedMeshedSurface -> meshedSurface for sampledTriSurfaceMesh

- all sampled surface types now consistently use the same storage,
  which allows some more simplifications in the future.

- before/after comparison of the sampledTriSurfaceMesh tested with
  motorbike passenger helmet (serial and parallel). Use the newly added
  'keepIds' functionality to retain the original ids, and can also
  compare them to the original obj file with "GenerateIds" in paraview.