System Status LED

[arandell93]

Refs #16

Per discussion in the above issue, it is desired that there be a status indicator LED onboard the boat so that the status of the system can be discerned at a glance without needing to read the wireless comms or SSH into the Pi.

The indicator will be used to provide basic information (via several flashing patterns) about the hardware and software readiness of the system. We may want to consider distinct indicators for:

• System OK (We can define exactly what this means as we move forward)
• System in Error (We can define exactly what this means as we move forward)
• System Shutting Down/Restarting

[whymarrh]

Note to self: I'm thinking of either moving this issue to the LakeMaps/pi or duplicating it there. I think it might make sense to have a level of indirection between the control software and the GPIO on the Pi. I'll worry about it when I tackle this.