altoslib/altosui: Carry receiver status around in AltosListenerState

This moves the crc_errors into the new structure and adds a receiver
battery voltage value there as well. Now the receiver status can be
monitored separately from the flight status. That also means that code
receiving state updates should be prepared to accept missing listener
or flight state values.

Signed-off-by: Keith Packard <keithp@keithp.com>