Flight plan fixes based on https://discordapp.com/channels/539048679160676382/539486309882789888/597133111272275970

* improved setting of combox value, fixed wrong text
* do NOT emit signals when same index
* getOwnCallsign
* do NOT used cache FPs for own aircraft

src/blackcore/context/contextownaircraftimpl.cpp

@@ -109,6 +109,12 @@ namespace BlackCore
             return m_ownAircraft.getTransponder();
         }
 
+        CCallsign CContextOwnAircraft::getOwnCallsign() const
+        {
+            QReadLocker l(&m_lockAircraft);
+            return m_ownAircraft.getCallsign();
+        }
+
         CCoordinateGeodetic CContextOwnAircraft::getOwnAircraftPosition() const
         {
             QReadLocker l(&m_lockAircraft);