functionObjects: Changed options 'outputControl' -> 'writeControl' and 'outputInterval' -> 'writeInterval'

for consistency with the time controls in controlDict and to avoid
unnecessary confusion.  All code and tutorials have been updated.

The old names 'outputControl' and 'outputInterval' are but supported for
backward compatibility but deprecated.

src/OpenFOAM/db/functionObjects/functionObjectList/functionObjectList.H

@@ -171,7 +171,7 @@ public:
         bool start();
 
         //- Called at each ++ or += of the time-loop. forceWrite overrides
-        //  the usual outputControl behaviour and forces writing always
+        //  the usual writeControl behaviour and forces writing always
         //  (used in post-processing mode)
         bool execute(const bool forceWrite = false);