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/xplane/simulatorxplane.cpp

@@ -577,6 +577,7 @@ namespace BlackSimPlugin
         {
             Q_ASSERT(isConnected());
             //! \todo XP driver obtain number of removed aircraft
+            resetHighlighting();
             int r = getAircraftInRangeCount();
             m_traffic->removeAllPlanes();
             updateMarkAllAsNotRendered();