Add license to src/xfce4-screensaver-configure

src/xfce4-screensaver-configure

 #!/usr/bin/python3
+# -*- Mode: Python; coding: utf-8; indent-tabs-mode: nil; tab-width: 4 -*-
+#   
+#   Copyright (C) 2019 Sean Davis <bluesabre@xfce.org>
+#
+#   This 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.
+#
+#   This program 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; if not, write to the Free Software
+#   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
+#
+#   Authors: Sean Davis <bluesabre@xfce.org
 
 import argparse
 import os