blink1: Sample HID app to control a blink(1) mk2 device.

This app demos the new chrome.hid API by controlling a blink(1) mk2 RGB
LED light. More interesting features (don't love RGB sliders?) coming soon!

http://blink1mk2.thingm.com/
`chrome.hid.getDevices` will always return an array. Therefore, it would be better to test `devices.length === 0`.