ENH: additional variants of IOobjectList findObject()

- cfindObject() for const pointer access.

- getObject() for mutable non-const pointer access, similar to the
     objectRegistry::getObjectPtr()

- cfindObject(), findObject(), getObject() with template type access
  to also check the headerClassName.

  For example,

      cfindObject("U")  ->  good
      cfindObject<volVectorField>("U") -> good
      cfindObject<volScalarField>("U") -> nullptr

  This allows inversion of looping logic.

    1) Obtain the names for a particular Type

       for (const word& objName : objs.sortedNames<Type>())
       {
           const IOobject* io = objs[objName];
           ...
       }

    2) Use previously obtained names and apply to a particular Type

       for (const word& objName : someListOfNames)
       {
           const IOobject* io = objs.cfindObject<Type>(objName);
           if (io)
           {
               ...
           }
       }

applications/utilities/postProcessing/lagrangian/steadyParticleTracks/steadyParticleTracks.C

@@ -27,7 +27,6 @@ Application
 Group
     grpPostProcessingUtilitie
 
-
 Description
     Generates a VTK file of particle tracks for cases that were computed using
     a steady-state cloud
@@ -84,7 +83,7 @@ label validateFields
     {
         if (ok[i])
         {
-            nOk++;
+            ++nOk;
         }
         else
         {