Bug fixes. AJE workarounds

- Change heat shield conductivity default to match Part heatConductivity
defaults (AJE workaround)
- Error trapping  for errors that were breaking KAS (and other mods
potentially)
- Allow engines to double ridiculousMaxTemp value
- Exempted engine overheating from scaring Kerbals.
- Added fix (hopefully) for edge cases involving flickering
AerodynamicsFX
- Check for DRE scenario null ref.