add PIUIO_Leds driver

The mappings in this driver are specific to the piuio kernel driver, but
once lights mapping is possible this could be made into a generic leds
class driver.
don't set lights for nonexistent lights

duh.
point at the right file in the filesystem
Merge pull request #276 from djpohly/piuio-leds

LightsDriver for /sys/class/leds with new PIUIO kernel module