Add UART control for LEDs and to reset the deck

[ataffanel]

The lighthouse deck has 4 LEDs, red, yellow and green, the intent is to use them to indicate the state of tracking. Since the Crazyflie is doing most of the job of tracking, the LEDs should be settable via the serial port.

A the same time, implementing a command to reset the FPGA in bootloader mode would be useful if we want to upgrade the FPGA bitstream while the Crazyflie is running (ie. using the radio) and if we want to save settings like the basestation geometry in the flash of the deck.