Make Pi code robust

[Phlosioneer]

• [x] Handle arduinos being plugged in during operation
• [x] Handle arduinos being unplugged
• [ ] Retain memory of arduinos being unplugged and then plugged back in
  • [x] Even when plugged back into a different port
  • [ ] Even when the Pi is rebooted
• [ ] Handle power loss
  • [x] Server starts when the pi boots
  • [ ] Arduinos work after boot (#290)
• [ ] Handle when arduinos draw too much power
• [x] Handle network failure
• [x] Handle arduino crashing

[BenMatase]

Is this still in progress?