Create LED controller subsystem

[danverstom]

Create subsystem which controls operation of the status LEDs

Note that the same subsystem is to be reused on the ground station, which only has 2 status LEDs. Account for this in the design.

In order to allow other subsystems to update the state of the LEDs, a LEDControlMessage SystemMessage should be implemented. This message could contain (suggestion only):

• The index of the LED to update
• The new colour to set the LED to

The MRAS_System class should have a field added called "led_subsystem" or similar so it knows which subsystem to sent LEDControlMessage messages to. MRAS_System should have control of one of the LEDs to indicate the overall status of all subsystems.

Enjoy flashing the LEDs!