ENH: added timeFunctionObject virtual class in inheritance hierarchy

- simply a functionObject with an additional Time reference, which is
  a combination frequently used by concrete functionObjects

src/functionObjects/utilities/timeActivatedFileUpdate/timeActivatedFileUpdate.C

@@ -89,8 +89,7 @@ Foam::functionObjects::timeActivatedFileUpdate::timeActivatedFileUpdate
     const dictionary& dict
 )
 :
-    functionObject(name),
-    time_(runTime),
+    timeFunctionObject(name, runTime),
     fileToUpdate_("unknown-fileToUpdate"),
     timeVsFile_(),
     lastIndex_(-1),
@@ -100,12 +99,6 @@ Foam::functionObjects::timeActivatedFileUpdate::timeActivatedFileUpdate
 }
 
 
-// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
-
-Foam::functionObjects::timeActivatedFileUpdate::~timeActivatedFileUpdate()
-{}
-
-
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 bool Foam::functionObjects::timeActivatedFileUpdate::read