Heading: Switch from Radians to Degrees

Work around quirkiness with ArduPilot and LOITER_* NaN handling on heading.

Hack around ArduPilot problems with unsupported NaN in Loiter commands

Default abort alt = 0. This works around problems between multi-rotor and fixed wing.

Added param2 for start video capture (update interval)
Excluded param2 above from PX4 as it's fixed to 0.2Hz
Re-added param2 test within CameraSectionTest (start video capture)

Fixed a pile of bugs as well

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