* Holds all the settings for the app
* Allows core plugin to override default values

Use component id from heartbeat

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

previously the start log button was always disabled, even for PX4.

Fixes regression from 9d413108

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

Prevent shutdown ordering crashes

PX4 doesn't retry commands by default

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