Miscellaneous fixes

* Command to set relays to the default configuration: power to cameras, no bypass power to heaters
* `snap` utility can now be initialized at the command line to specified exposure time and gains
* A boolean in the telemetry packet reports whether a good GPS packet has been received since the previous telemetry packet
* Fixed bug where the while loop in main() was missing a sleep call, which caused unnecessary load on the processor
* Command to restart the flight executable by quitting the running executable and letting systemd restart it

Merging immediately