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/blackmisc/simulation/airspaceaircraftsnapshot.h

@@ -83,12 +83,16 @@ namespace BlackMisc
             //! \copydoc CValueObject::convertToQString
             QString convertToQString(bool i18n = false) const;
 
+            //! Generating thread name
+            const QString &generatingThreadName() const { return m_threadName; }
+
         private:
             BLACK_ENABLE_TUPLE_CONVERSION(CAirspaceAircraftSnapshot)
             qint64 m_timestampMsSinceEpoch = -1;
             bool m_restricted = false;
             bool m_restrictionChanged = false;
             bool m_renderingEnabled = true;
+            QString m_threadName; //!< generating thread name for debugging purposes
 
             // remark closest aircraft always first
             BlackMisc::Aviation::CCallsignSet m_aircraftCallsignsByDistance;