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/
When a blink1 device is not plugged, `chrome.runtime.lastError` is not set.
Not sure if it's intended or a bug there.