feat(mail): initial support for ms-tnef (winmail.dat) body part

Fixes #2242
Fixes #4503

UI/MailPartViewers/UIxMailPartTNEFViewer.h

@@ -0,0 +1,33 @@
+/* UIxMailPartTNEFViewer.h - this file is part of SOGo
+ *
+ * Copyright (C) 2021 Inverse inc.
+ *
+ * This file 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, or (at your option)
+ * any later version.
+ *
+ * This file 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 this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#ifndef UIXMAILPARTTNEFVIEWER_H
+#define UIXMAILPARTTNEFVIEWER_H
+
+#import "UIxMailPartMixedViewer.h"
+
+@interface UIxMailPartTNEFViewer : UIxMailPartMixedViewer
+{
+}
+
+
+@end
+
+#endif /* UIXMAILPARTTNEFVIEWER_H */