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");

applications/solvers/multiphase/VoF/alphaCourantNo.H

@@ -31,7 +31,7 @@ Description
 
 scalar maxAlphaCo
 (
-    readScalar(runTime.controlDict().lookup("maxAlphaCo"))
+    runTime.controlDict().get<scalar>("maxAlphaCo")
 );
 
 scalar alphaCoNum = 0.0;