Update rpi-rgb-led-matrix to point to own fork

I modified the sources a bit so that I could use some general classes
without having to reimplement them myself.
Implement display class for the binary clock.

Currently, the display class, LedClock, in the led-clock sources, reports the
current time with a string in little endian binary, using a BinaryDate as a
backend. This string will be used to set the LEDs when the LED matrix is
connected.