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

clients/lcdvc/lcdvc.conf

@@ -18,6 +18,9 @@
 # run in foreground [default: false; legal: true, false]
 #Foreground=false
 
+# PidFile location when running as daemon [default: /var/run/lcdvc.pid]
+#PidFile=/var/run/lcdvc.pid
+
 # Keys to move the visible area around the screen.
 #UpKey=Up
 #DownKey=Down