Change implementation of low level watchdog

[ramensandwich]

Currently if the watchdog barks (times out), then it will drop the brakes and spin in a loop. In order to continue, the system will need to be reset. Instead, low level should drop brakes and reset the system. Additionally, on startup low level should check the MCUSR (MCU Status Register) and set the appropriate bit for the cause of the reset. This will be reported to high level until the system receives a physical reset.