Add script for systemd (Guthub #434)

ejabberd.service.template

+[Unit]
+Description=XMPP Server
+After=network.target
+
+[Service]
+User=ejabberd
+Group=ejabberd
+LimitNOFILE=16000
+RestartSec=5
+ExecStart=/bin/sh @ctlscriptpath@/ejabberdctl start
+ExecStop=@ctlscriptpath@/ejabberdctl stop
+ExecReload=@ctlscriptpath@/ejabberdctl reload_config
+Type=oneshot
+RemainAfterExit=yes
+
+[Install]
+WantedBy=multi-user.target