ENH: define IOobjectList::csorted(), deprecate some sorted() const methods

- prefer csorted() method for const access since it ensures that the
  return values are also const pointers (for example) even if
  the object itself can be accessed as a non-const.

- the csorted() method already existed for HashTable and
  objectRegistry, but now added to IOobjectList for method name
  consistency (even although the IOobjectList only has a const-access
  version)

ENH: objectRegistry with templated strict lookup

- for lookupClass and csorted/sorted. Allows isType restriction as a
  compile-time specification.

src/OpenFOAM/containers/HashTables/HashTable/HashTable.C

@@ -192,14 +192,6 @@ Foam::HashTable<T, Key, Hash>::csorted() const
 }
 
 
-template<class T, class Key, class Hash>
-Foam::UPtrList<const typename Foam::HashTable<T, Key, Hash>::node_type>
-Foam::HashTable<T, Key, Hash>::sorted() const
-{
-    return csorted();
-}
-
-
 template<class T, class Key, class Hash>
 Foam::UPtrList<typename Foam::HashTable<T, Key, Hash>::node_type>
 Foam::HashTable<T, Key, Hash>::sorted()