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");

etc/codeTemplates/BC/BC.C

@@ -73,7 +73,7 @@ CONSTRUCT
 )
 :
     PARENT(p, iF),
-    scalarData_(readScalar(dict.lookup("scalarData"))),
+    scalarData_(dict.get<scalar>("scalarData")),
     data_(pTraits<TYPE>(dict.lookup("data"))),
     fieldData_("fieldData", dict, p.size()),
     timeVsData_(Function1<TYPE>::New("timeVsData", dict)),