refs #395, improvements for snapshot / restricted aircraft handling

* fixed isCurrentThreadCreatingThread and renamed to isCurrentThreadObjectThread (this check was never working), added 2 more thread checks
* changed remove aircraft function to return number of returned aircraft (like with the containers this allows to avoid unnecessary signals)
* removed unused function ps_recalculateRenderedAircraft() / SimulatorCommon
* using Queued airspaceAircraftSnapshot signal for binding (functor connect does not provide connection type)
* extened ASSERTs to check threads
* simulator: initial situation function with return value (success?)
* simulator: avoid unneccessary copy and provide correct rendered flag in add aircraft function

src/blackcore/airspace_monitor.h

@@ -197,6 +197,9 @@ namespace BlackCore
         //! An aircraft disappeared
         void removedAircraft(const BlackMisc::Aviation::CCallsign &callsign);
 
+        //! \copydoc CAirspaceAnalyzer::airspaceAircraftSnapshot
+        void airspaceAircraftSnapshot(const BlackMisc::Simulation::CAirspaceAircraftSnapshot &snapshot);
+
     private:
         BlackMisc::Aviation::CAtcStationList m_atcStationsOnline;
         BlackMisc::Aviation::CAtcStationList m_atcStationsBooked;