Improve/Fix SBS-1 ADS-B Parsing

[MUSTARDTIGERFPV]

tl;dr: add ground track, speed, callsign, squawk codes, fix math error causing altitude discrepancy.

While writing https://github.com/MUSTARDTIGERFPV/MavADSB I discovered a few quirks about the ADS-B SBS-1 processing in Mission Planner. This PR addresses those quirks.

1. Ground track, speed, callsign, are parsed in SBS-1 message types one and four, but UpdatePlanePosition is called only in type 3. Its ground speed was fixed to -1, and the callsign wasn't set at all. This changes that behavior so all fields get updated as soon as a type 3 is seen using the values stored from the type 1 and type 4 messages.
2. Squawk codes were not interpreted at all - they've been added.
3. Previously, the altitude value sent OTA was divided by a factor which represents the number of meters in 10ft. Given that ADS-B Mode C altitudes are given in feet, and the PointLatLngAltHdg's internal representation is in meters, the correct conversion factor is approximately 3.28, the number of feet in a meter. This change makes Mission Planner's altitudes match those of https://globe.adsb-exchange.com and https://globe.adsb.one. The previous math would look correct for lower altitudes, but would skew more and more the higher a plane got. For example, at 32000 ft, it's a difference between 9753m and 10499m, 746m off.

There's a chance other protocols will need their altitude math looked at also, but I've not taken a look at it just yet.