snappyHexMesh: Added "noRefinement" writeFlag to control the writing of cellLevel, pointLevel etc. files

By default snappyHexMesh writes files relating to the hex-splitting process into
the polyMesh directory: cellLevel level0Edge pointLevel surfaceIndex

but by setting the noRefinement flag:

writeFlags
(
    noRefinement
    .
    .
    .
);

these optional files which are generally not needed are not written.

If you run the three stages of snappyHexMesh separately or run a dynamic mesh
solver supporting refinement and unrefinement these files are needed
and "noRefinement" should not be set.

tutorials/incompressible/simpleFoam/windAroundBuildings/system/snappyHexMeshDict

@@ -87,14 +87,14 @@ addLayersControls
 }
 
 meshQualityControls
-{
-}
+{}
 
 writeFlags
 (
-    scalarLevels
-    layerSets
-    layerFields
+    noRefinement
+    // scalarLevels
+    // layerSets
+    // layerFields
 );
 
 mergeTolerance 1e-6;