Added comment for dummy variable in vehicle.cc.  Enabled _firmwarePlugin call that shows 'Landing aborted.' message.

- Shot Interval in Survey
- Much change to time/distance calc

Prevent shutdown ordering crashes

Also changed GPS FactGroup values to use NaN appropriately to show
unavailable values.

altitudeAMSL and altitudeRelative do not need divide 1000，the unit is meter and float format。 can you use _handleGlobalPositionInt message for altitudeAMSL and altitudeRelative？ because _handleGlobalPositionInt is default 5Hz and _handleAltitude is 1Hz.

* Moved from UAS
* Remove unused code

The return lead to data being dropped. Some of this data could have been
part of the ulog header, which lead to corrupt files.

Forcing QGC to use Mavlink V2 if vehicle supports it.

Also added new FirmwarePlugin::brandImage support

_finalize methods need information which is not available if all you
have is a mavlink_message_t