Reflecting discussed changes for interpolation performance refs #386

(based on FSX testing)
* Only send changed situation to SIM
* Split sending of parts / situations
* Only send parts with a reduced frequency (means slower as positions)
* Mark geodetic height as null for default values (the value is usually unavailable)
* Fixed altitude to MSL for network data
* Trace which aircrafts support aircraft parts via network
* Renamed insert_fron push_front (as proposed by Roland)

Status quo / lessons learnt
* On slower PCs jitter is still noticed for interpolated aircraft.
* Running interpolation in an independent process (aka core, not in GUI) reduced load dependencies
  => it seems to make sense to run driver in own thread
* The onGround flag in parts seems clumsy as it required to retrieve parts for position updates
* In interpolation performance really matters

src/blackmisc/simulation/simulatedaircraftlist.h

@@ -43,6 +43,9 @@ namespace BlackMisc
             //! All pilots (with valid data)
             BlackMisc::Network::CUserList getPilots() const;
 
+            //! Callsigns of aircraft with synchronized parts
+            BlackMisc::Aviation::CCallsignList getCallsignsWithSyncronizedParts() const;
+
             //! \copydoc CValueObject::toQVariant
             virtual QVariant toQVariant() const override { return QVariant::fromValue(*this); }