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/compressibleMultiphaseInterFoam/multiphaseMixtureThermo/multiphaseMixtureThermo.C

@@ -763,8 +763,8 @@ void Foam::multiphaseMixtureThermo::solve()
     const Time& runTime = mesh_.time();
 
     const dictionary& alphaControls = mesh_.solverDict("alpha");
-    label nAlphaSubCycles(readLabel(alphaControls.lookup("nAlphaSubCycles")));
-    scalar cAlpha(readScalar(alphaControls.lookup("cAlpha")));
+    label nAlphaSubCycles(alphaControls.get<label>("nAlphaSubCycles"));
+    scalar cAlpha(alphaControls.get<scalar>("cAlpha"));
 
     volScalarField& alpha = phases_.first();