Feature Request: Add GPS state info to RepeaterStats frame

[cwichura]

It'd be really nice if we could get GPS state from a repeater without having to remote cli the "gps" command.

So I propose adding two values to the RepeaterStats frame:

1. A byte with the highest bit flagging if GPS is turned on or off. The remaining lower bits indicate the number of sats in the last fix, or 0 if GPS is turned off.
2. The time of the last fix in unixtime. If there is no current fix, returns 0.

Using 0 for the time of last fix when there is no current fix doubles as a way to explicitly say there is no current fix without consuming an additional status bit to encode that flag.