Update scanner instructions

app/static/img/xenon/activate-custom-defaults.png

app/static/img/xenon/daytime-mode.png

app/static/img/xenon/hand-held-scanning.png

app/static/img/xenon/rs232-interface.png

app/static/img/xenon/silent-mode-with-flashing-led.png

app/static/img/xenon/usb-keyboard-mac.png

app/static/img/xenon/usb-keyboard-pc.png

app/static/img/xenon/usb-serial.png

app/templates/inventory/scanner.html