add node class used by stack

@node/data.m

+function val = data(self)
+
+% get access methods for properties 
+% ---------------------------------   
+val = self.data;	
+

@node/get.m

+function val = get(self, arg)
+
+% get access methods for properties 
+% ---------------------------------   
+switch arg
+case 'data'
+  val = self.data;	
+case 'next'
+  val = self.next;
+otherwise
+    error('Wrong input args');
+end
+

@node/next.m

+function val = next(self)
+
+% get access methods for properties 
+% ---------------------------------   
+val = self.next;	
+

@node/node.m

+function n = node(data,next)
+% node.m
+%
+% This class is used with stack class to implemete LIFO stack
+%
+% $Id$
+
+%% COPYRIGHT & LICENSE
+%  Copyright 2009 - IRD US191, all rights reserved.
+%
+%  This file is part of tsg-qc Matlab program.
+%
+%    tsg-qc program is free software; you can redistribute it and/or modify
+%    it under the terms of the GNU General Public License as published by
+%    the Free Software Foundation; either version 2 of the License, or
+%    (at your option) any later version.
+%
+%    tsgqc is distributed in the hope that it will be useful,
+%    but WITHOUT ANY WARRANTY; without even the implied warranty of
+%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+%    GNU General Public License for more details.
+%
+%    You should have received a copy of the GNU General Public License
+%    along with Datagui; if not, write to the Free Software
+%    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
+%    USA
+
+if nargin == 2
+  self.data = data;
+  self.next = next;
+else
+  self.data = {};
+  self.next = {};	
+end
+
+% class constructor
+% -----------------
+n = class(self, 'node');