- treat 'ofs' IO just like any other format
- dropped BasicMeshedSurface, since MeshedSurface can now also have zero or
  more zones
- UnsortedMeshedSurface is a special type of MeshedSurface with zero zones,
  but with additional zoneId labels
- use MeshedSurfaceProxy for writing surfaces with points/faces/zones and
  optional faceMap - provides output interface for MeshedSurface,
  UnsortedMeshedSurface and surfMesh.
- simplify output to filenames only, I can't see that the Ostream
  is needed anywhere
- surfMesh renaming now works, after the objectRegistry fix