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/engine/include/StCorr.H

@@ -18,12 +18,9 @@
                     // Assume it is part-spherical
                     scalar sphereFraction
                     (
-                        readScalar
+                        combustionProperties.get<scalar>
                         (
-                            combustionProperties.lookup
-                            (
-                                "ignitionSphereFraction"
-                            )
+                            "ignitionSphereFraction"
                         )
                     );
 
@@ -47,12 +44,9 @@
 
                     scalar circleFraction
                     (
-                        readScalar
+                        combustionProperties.get<scalar>
                         (
-                            combustionProperties.lookup
-                            (
-                                "ignitionCircleFraction"
-                            )
+                            "ignitionCircleFraction"
                         )
                     );