Ref T232, aircraft can be re-added or removed via "dot-commands"

* can be used for testing
* utility functions to find inconsistent aircraft states
* reset highlight state

src/plugins/simulator/fs9/simulatorfs9.cpp

@@ -206,6 +206,7 @@ namespace BlackSimPlugin
 
         int CSimulatorFs9::physicallyRemoveAllRemoteAircraft()
         {
+            resetHighlighting();
             if (m_hashFs9Clients.isEmpty()) { return 0; }
             QList<CCallsign> callsigns(m_hashFs9Clients.keys());
             int r = 0;