Printing all queued messages when button is pressed

- Will send each item in queue to printer
- Stops flashing LED when no items left in queue
- Bring 'things' library into project for interfacing Button/LED
Catch and log HTTP errors to console
Fix bug where things.LED was hardcoded to pin 7
Blink 2 LEDs and play sound when messages waiting
Better logging in printer app
Merge branch 'js' of https://github.com/andrewn/raspi-printer into js