bin/adjust-volume: add 2 commands to turn on/off audio
bin/lock-screen: dpms usage is more advanced than I thought
bin/xscreensaver-watcher: watch the screensaver and turn off screen/sound
bin/xscreensaver-watcher: basically copied from the xscreensaver-command man page

Signed-off-by: Bao Haojun <baohaojun@gmail.com>