Re-implement the light class to use GPIO

[cal-pratt]

Instead of a Maestro for lights we're going to use a GPIO.

Steps:

• Remove the existing Light class and and tests from the project.
• Create a Light interface in the devices package. The flash method should do the same thing as the existing light class; just change between on/off at the same frequency.

public interface Light {
    void write(final boolean active);
    void flash();
}

• Implement the interface using a pi4j gpio object. Place this in the io.rpi package. Some name like RaspberryGpioLight
• Add the light channel to the config.
• Add the light to the Rov ctor and manage.

SpeedValue no longer really works; the value is a boolean not a float range. For now you can just map the speedvalue to a boolean, until you recreate the lights value fully.

eventPublisher.valuesOfType(LightASpeedValue.class)
    .startWith(new LightASpeedValue())
    .map(SpeedValue::getSpeed)
    .map(v -> v > 0.5)