functionObjects: Moved into the functionObjects namespace and rationalized and simplified failable construction

Rather than requiring each functionObject to handle failed construction
internally (using the active_ flag) the static member function "viable"
is provided which returns true if construction of the functionObject is
likely to be successful.  Failed construction is then handled by the
wrapper-class which constructs the functionObject,
e.g. "OutputFilterFunctionObject".

src/postProcessing/functionObjects/IO/removeRegisteredObject/removeRegisteredObject.H

@@ -22,7 +22,7 @@ License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
 Class
-    Foam::removeRegisteredObject
+    Foam::functionObjects::removeRegisteredObject
 
 Group
     grpIOFunctionObjects
@@ -128,9 +128,9 @@ public:
             const bool loadFromFiles = false
         );
 
-        //- Construct on free-store and return pointer if successful
-        //  otherwise return a null-pointer
-        static autoPtr<removeRegisteredObject> New
+        //- Return true if the construction of this functionObject is viable
+        //  i.e. the prerequisites for construction are available
+        static bool viable
         (
             const word& name,
             const objectRegistry&,