led controller: port to teensy 3.1

 - For now, only target the teensy 3.1.
 - Target full 16-bit pwm (not sure if clock set correctly for full use
   though)
 - Eliminate color correction code
   - Likely wrong anyway
 - Revert to simple text based protocol
   - Teensy I/O is buffered, this is easier
 - Blink random colors when no device has the serial port open