ENH: use meshedSurf API for surface writers (issue #104)

- Allows passing of additional information (per-face zone ids) or possibly
  other things, while reducing the number of arguments to pass.

- In sampledTriSurfaceMesh, preserve the region information that was
  read in, passing it onwards via the UnsortedMeshSurface content.

  The Nastran surface writer is currently the only writer making use
  of this per-face zone information.
  Passing it through as a PSHELL attribute, which should retain the
  distinction for parts. (issue #204)

src/functionObjects/field/fieldValues/surfaceFieldValue/surfaceFieldValueTemplates.C

@@ -328,8 +328,11 @@ bool Foam::functionObjects::fieldValues::surfaceFieldValue::writeValues
                 (
                     outputDir(),
                     regionTypeNames_[regionType_] + ("_" + regionName_),
-                    points,
-                    faces,
+                    meshedSurfRef
+                    (
+                        points,
+                        faces
+                    ),
                     fieldName,
                     allValues,
                     false