FlightGear - Flight Simulator FGAddon

* Systems/Lockheed1049h-views.xml: remove the pilot view.
* Lockheed1049h-common.xml: new. Factorize most of the pilot (regular)
and copilot models.
* Nasal/Gidenstam/{,co}pilot-dual-control.nas: delete, superseded by
common aircraft files.
* Lockheed1049h-set.xml:
- include Lockheed1049h-common.xml.
- declare the pilot view.
- load Aircraft/Generic/DualControl/pilot-dual-control.nas.
* Lockheed1049h-copilot-set.xml:
- include Lockheed1049h-common.xml.
- declare the copilot view as main.
- load Aircraft/Generic/DualControl/copilot-dual-control.nas.

The copilot is still only a passenger but things are cleaner now.