FlightGear - Flight Simulator FGAddon

- Add missing prev-target select (shift-y)
- Revise add/remove fuel algorithm to maintain better tank balancing.
- CADC: added pitch trim compensator
- CADC: tuned pitch ratio to achieve more consistent g->stick position across flight envelope
- Remove setting of default-model property (as it doesn't work properly so keep the core default (glider))
- Remove unused files.