Automatically shut down a printer after a while if idle

This is for people who use [OctoPrint](http://octoprint.org/) and have connected their printer to a relay board, like explained [here](https://www.thingiverse.com/thing:1428478) by [Jeffeb3](https://www.thingiverse.com/Jeffeb3).

After applying this tutorial, OctoPrint will be able to automatically shut down your printer *only* if in an idle state. It also works for lighting, etc. In short, anything you could have plugged to your relay board.