ENH: make 'planeType' optional for dictionary construct of a plane

- simpler to write for sampled cutting planes etc.
  For example,

      slice
      {
          type        cuttingPlane;
          point       (0 0 0);
          normal      (0 0 1);
          interpolate true;
      }

  instead of

      slice
      {
          type        cuttingPlane;
          planeType   pointAndNormal;
          pointAndNormalDict
          {
              point   (0 0 0);
              normal  (0 0 1);
          }
          interpolate true;
      }

STYLE: add noexcept to some plane methods

tutorials/heatTransfer/solidFoam/movingCone/system/cuttingPlane

@@ -16,14 +16,10 @@ cuttingPlane
     {
         zNormal
         {
-            type            cuttingPlane;
-            planeType       pointAndNormal;
-            pointAndNormalDict
-            {
-                point   (0 0 0);
-                normal  (0 0 1);
-            }
-            interpolate     true;
+            type        cuttingPlane;
+            point       (0 0 0);
+            normal      (0 0 1);
+            interpolate true;
         }
     }
 }