ENH: avoid readScalar, readLabel etc from dictionary (#762, #1033)

- use the dictionary 'get' methods instead of readScalar for
  additional checking

     Unchecked:  readScalar(dict.lookup("key"));
     Checked:    dict.get<scalar>("key");

- In templated classes that also inherit from a dictionary, an additional
  'template' keyword will be required. Eg,

     this->coeffsDict().template get<scalar>("key");

  For this common use case, the predefined getXXX shortcuts may be
  useful. Eg,

     this->coeffsDict().getScalar("key");

src/parallel/decompose/decompositionMethods/decompositionMethod/decompositionMethod.C

@@ -57,7 +57,7 @@ namespace Foam
 
 Foam::label Foam::decompositionMethod::nDomains(const dictionary& decompDict)
 {
-    return readLabel(decompDict.lookup("numberOfSubdomains"));
+    return decompDict.get<label>("numberOfSubdomains");
 }