ENH: region-wise decomposition specification for decomposeParDict

Within decomposeParDict, it is now possible to specify a different
  decomposition method, methods coefficients or number of subdomains
  for each region individually.

  The top-level numberOfSubdomains remains mandatory, since this
  specifies the number of domains for the entire simulation.
  The individual regions may use the same number or fewer domains.

  Any optional method coefficients can be specified in a general
  "coeffs" entry or a method-specific one, eg "metisCoeffs".

  For multiLevel, only the method-specific "multiLevelCoeffs" dictionary
  is used, and is also mandatory.

----

ENH: shortcut specification for multiLevel.

  In addition to the longer dictionary form, it is also possible to
  use a shorter notation for multiLevel decomposition when the same
  decomposition method applies to each level.

applications/utilities/parallelProcessing/decomposePar/decomposePar.C

@@ -330,7 +330,6 @@ int main(int argc, char *argv[])
     }
 
 
-
     forAll(regionNames, regioni)
     {
         const word& regionName = regionNames[regioni];
@@ -338,13 +337,12 @@ int main(int argc, char *argv[])
 
         Info<< "\n\nDecomposing mesh " << regionName << nl << endl;
 
-
         // Determine the existing processor count directly
         label nProcs = fileHandler().nProcs(runTime.path(), regionDir);
 
-        // Get requested numberOfSubdomains. Note: have no mesh yet so
-        // cannot use decompositionModel::New
-        const label nDomains = readLabel
+        // Get requested numberOfSubdomains directly from the dictionary.
+        // Note: have no mesh yet so cannot use decompositionModel::New
+        const label nDomains = decompositionMethod::nDomains
         (
             IOdictionary
             (
@@ -362,7 +360,7 @@ int main(int argc, char *argv[])
                     ),
                     decompDictFile
                 )
-            ).lookup("numberOfSubdomains")
+            )
         );
 
         if (decomposeFieldsOnly)