improve refined and smooth mesh script

[Thomas-Ulrich]

• use pygalmesh to first remesh the surface mesh (useful if the initial surface mesh is very bad).
• allow smoothing and keeping boundary nodes unchanged.
  Example: initial very bad mesh:
  
  mesh smoothed and refined with previous code:
  
  mesh smoothed and refined with new --fix_boundary option:
  

mesh remeshed with pygal (no smoothing):