Ref T270, Ref T268, plugin common / simulator improvements

* connect with "about to quit"
* added interface declarations
* sim statistics, use common function setStatsRemoteAircraftUpdate and double for average values

src/plugins/simulator/fscommon/simulatorfscommon.cpp

@@ -85,7 +85,7 @@ namespace BlackSimPlugin
             // reset flags
             m_simPaused = false;
             this->emitSimulatorCombinedStatus();
-            return true;
+            return CSimulatorPluginCommon::disconnectFrom();
         }
 
         bool CSimulatorFsCommon::isFsuipcConnected() const