ENH: make PDRsetField ground, outer patch names configurable

- previously hard-coded, now adjustable within PDRsetFieldsDict

    // Change some predefined patch names
    patchNames
    {
        ground      ground;
        outer       outer;
    }

ENH: additions to PDRutils, improve comments

- expose enumerated expansion names and gridControl (PDRblock).
  Not commonly needed, but useful to have access when defining
  other grid generators

TUT: update PDRsetFieldsDict and tutorials to use "ground"

- remove tutorial references to unused types and legacy obstacles

- use "ground" for the boundary conditions instead of "seaGround".
  Consistent with PDRblockMesh

applications/utilities/preProcessing/PDR/pdrFields/PDRparams.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -84,6 +84,20 @@ void Foam::PDRparams::readDefaults(const dictionary& dict)
     dict.readIfPresent("blockageNoCT", blockageNoCT);
     dict.readIfPresent("scale", scale);
 
+
+    const dictionary* dictptr;
+
+    groundPatchName = "ground";
+    outerPatchName = "outer";
+
+    if ((dictptr = dict.findDict("patchNames")) != nullptr)
+    {
+        const dictionary& d = *dictptr;
+
+        d.readIfPresent("ground", groundPatchName);
+        d.readIfPresent("outer", outerPatchName);
+    }
+
     UPatchBc = "fixedValue;value uniform (0 0 0)";
     if (dict.readIfPresent("UPatchBc", UPatchBc))
     {