Change clearing the LEDs to an interrupt.

This required a few changes - the movement of the success and failure
LEDs from pins (2, 3) to pins (4, 5) to clear up pins (2, 3) - the first
for the current interrupt, the second reserved for future use.
Improve debug functionality.
Remove off switch.

It doesn't actually do anything besides forcing a quick loop. Easier and
smarter to just unplug the thing.