Store device identifier and broker in non-volatile memory

[ryan-summers]

Currently, stabilizer generates an identifier using the binary name and MAC address. We should allow this default to be overridden by the user and the value should persist to non-volatile memory.

Using the unused flash bank for storage should be sufficient.

This is a follow-on to #276

[jordens]

And in the same way we would store the broker (dns name or IP).

[ryan-summers]

We also would want to store application-specific settings as well, e.g. for driver, as noted by @nkrackow

[ryan-summers]

This will likely also necessitate the addition of a serial terminal to stabilizer to facilitate configuration of the initial network parameters. We may want to leverage some of the serial code on Booster for this