refs #780, signal installedAircraftModelsChanged dangling

* discovered during testing, signal is not used (since we now use model set)
* renamed context signal to "modelSetChanged"
* prepared context for message settings

src/blackcore/simulator.h

@@ -191,9 +191,6 @@ namespace BlackCore
         //! Aircraft rendering changed
         void aircraftRenderingChanged(const BlackMisc::Simulation::CSimulatedAircraft &aircraft);
 
-        //! Installed aircraft models ready or changed
-        void installedAircraftModelsChanged();
-
         //! An airspace snapshot was handled
         void airspaceSnapshotHandled();