Switch FixedPrec fromRational to floor from round

Because (1) this is what Fixed does, and (2) the blink(1) device actually adds
1cs to every delay and then rounds down to the next cycle, so this is a closer
correction when converting from floats.
Make blink work on individual mk2 LEDs

This was a little messy due to the broken setColor2 call.  We use fadeColor2
instead, but then have to wait 1cs before sending another command to make sure
it takes effect.