added typedef for first order Triangle in Tri.h

MeshLib/Elements/Tri.h

+/**
+ * Copyright (c) 2012, OpenGeoSys Community (http://www.opengeosys.net)
+ *            Distributed under a Modified BSD License.
+ *              See accompanying file LICENSE.txt or
+ *              http://www.opengeosys.org/LICENSE.txt
+ *
+ * \file Tri.h
+ *
+ *  Created on  Sep 27, 2012 by Thomas Fischer
+ */
+
+#ifndef TRI_H_
+#define TRI_H_
+
+#include "TemplateTri.h"
+
+namespace MeshLib {
+
+typedef TemplateTri<1,3> Tri;
+
+}
+
+#endif /* TRI_H_ */