ENH: overhaul ensight handling (#1579)

- includes restructuring and simplification of low-level ensight part
  handling and refactor of backends to improve code reuse.

foamToEnsight
-------------

  * new cellZone support.
    This was previously only possible via a separate foamToEnsightParts
    utility that was not parallelized.

  * support for point fields.

  * `-nearCellValue` option (as per foamToVTK)

  * data indexing now uses values from the time index.
    This is consistent with the ensightWrite function object and
    can help with restarts.

  * existing ensight directories are removed, unless the -no-overwrite
    option is supplied

foamToEnsightParts
------------------
  * now redundant and removed.

ensightOutputSurface (new class)
--------------------------------
  * a lightweight wrapper for point/face references that is tailored
    for the ensightSurfaceWriter. It uses compact face/point information
    and is serial only, since this is the format requirements from the
    surfaceWriter class.

ensightMesh (revised class)
---------------------------
  * now only holds a polyMesh reference, which removes its dependency
    on finiteVolume and allows it to be relocated under fileFormats
    instead of conversion.

Removed classes: ensightParts, ensighPartFaces, ensightPartCells

- these were used by foamToEnsightParts, but not needed anymore.

src/functionObjects/utilities/ensightWrite/ensightWrite.C

@@ -77,7 +77,8 @@ Foam::functionObjects::ensightWrite::ensightWrite
 )
 :
     fvMeshFunctionObject(name, runTime, dict),
-    writeOpts_
+    writeOpts_(),
+    caseOpts_
     (
         IOstreamOption::formatNames.lookupOrDefault
         (
@@ -87,7 +88,6 @@ Foam::functionObjects::ensightWrite::ensightWrite
             true  // Failsafe behaviour
         )
     ),
-    caseOpts_(writeOpts_.format()),
     outputDir_(),
     consecutive_(false),
     meshState_(polyMesh::TOPO_CHANGE),

src/functionObjects/utilities/ensightWrite/ensightWriteTemplates.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2016-2019 OpenCFD Ltd.
+    Copyright (C) 2016-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -58,9 +58,9 @@ Foam::label Foam::functionObjects::ensightWrite::writeVolFields
 
         ensightOutput::writeVolField<Type>
         (
+            os.ref(),
             field,
             ensMesh(),
-            os.ref(),
             caseOpts_.nodeValues()
         );