functionObjects: layerAverage: Replacment for postChannel

This function generates plots of fields averaged over the layers in the
mesh. It is a generalised replacement for the postChannel utility, which
has been removed. An example of this function's usage is as follows:

    layerAverage1
    {
        type            layerAverage;
        libs            ("libfieldFunctionObjects.so");

        writeControl    writeTime;

        setFormat       raw;

        // Patches and/or zones from which layers extrude
        patches         (bottom);
        zones           (quarterPlane threeQuartersPlane);

        // Spatial component against which to plot
        component       y;

        // Is the geometry symmetric around the centre layer?
        symmetric       true;

        // Fields to average and plot
        fields          (pMean pPrime2Mean UMean UPrime2Mean k);
    }

tutorials/incompressible/pimpleFoam/LES/channel395/Allrun

@@ -17,6 +17,4 @@ runApplication decomposePar -cellDist
 runParallel $application
 runApplication reconstructPar
 
-runApplication postChannel
-
 #------------------------------------------------------------------------------

tutorials/incompressible/pimpleFoam/LES/channel395/system/controlDict

@@ -47,6 +47,31 @@ runTimeModifiable true;
 functions
 {
     #includeFunc fieldAverage(U, p, prime2Mean = yes)
+
+    #includeFunc uniform
+    (
+        fieldType = volScalarField,
+        name = half,
+        dimensions = [0 0 0 0 0 0 0],
+        value = 0.5
+    )
+
+    #includeFunc mag(UPrime2Mean)
+
+    #includeFunc multiply(half, mag(UPrime2Mean), result = k)
+
+    #includeFunc graphLayerAverage
+    (
+        funcName = layerAverage,
+        patches = (bottomWall),
+        axis = y,
+        symmetric = yes,
+        pMean,
+        pPrime2Mean,
+        UMean,
+        UPrime2Mean,
+        k
+    );
 }
 
 // ************************************************************************* //