add PID file handling to clients (including signal handling to remove the files)

clients/lcdexec/lcdexec.conf

@@ -17,6 +17,9 @@ ReportToSyslog=false
 # run in foreground [default: false; legal: true, false]
 Foreground=false
 
+# PidFile location when running as daemon [default: /var/run/lcdexec.pid]
+#PidFile=/var/run/lcdexec.pid
+
 # shell to use for executing programsi
 # [default: $SHELL or /bin/sh; legal: any shell that understands: -c COMMAND]
 #Shell=/bin/sh