[xswiftbus] Replace QtDBus with a libevent driven C++ wrapper on top of libdbus

QtDBus was the main component of xswiftbus' Qt dependency. This is the
first preparation step to get xswiftbus Qt free.
The new implementation is based on the low level libdbus library, which
was also in use by QtDBus itself. But instead of QtDBus, we use now a thin
C++ wrapper. To keep DBus handling async, libevent is used to monitor
timeouts and fds.

src/xswiftbus/traffic.h

@@ -12,6 +12,7 @@
 
 //! \file
 
+#include "dbusobject.h"
 #include "datarefs.h"
 #include "terrainprobe.h"
 #include <QDateTime>
@@ -34,14 +35,11 @@ namespace XSwiftBus
     /*!
      * XSwiftBus service object for traffic aircraft which is accessible through DBus
      */
-    class CTraffic : public QObject
+    class CTraffic : public CDBusObject
     {
-        Q_OBJECT
-        Q_CLASSINFO("D-Bus Interface", XSWIFTBUS_TRAFFIC_INTERFACENAME)
-
     public:
         //! Constructor
-        CTraffic(QObject *parent);
+        CTraffic(CDBusConnection *dbusConnection);
 
         //! Destructor
         virtual ~CTraffic();
@@ -63,14 +61,6 @@ namespace XSwiftBus
         //! Called by XPluginStart
         static void initLegacyData();
 
-    signals:
-        //! Signal emitted for each simulator rendering frame
-        void simFrame();
-
-        //! Remote aircraft data
-        void remoteAircraftData(const QString &callsign, double latitude, double longitude, double elevation, double modelVerticalOffset);
-
-    public slots:
         //! Initialize the multiplayer planes rendering and return true if successful
         bool initialize();
 
@@ -117,11 +107,17 @@ namespace XSwiftBus
         //! Request traffic plane data. A signal remoteAircraftData will be emitted for each known plane
         void requestRemoteAircraftData();
 
+        int processDBus() override;
+
+    protected:
+         DBusHandlerResult dbusMessageHandler(const CDBusMessage &message) override;
+
     private:
         bool m_initialized = false;
         bool m_enabled = false;
 
         void emitSimFrame();
+        void emitRemoteAircraftData(const QString &callsign, double latitude, double longitude, double elevation, double modelVerticalOffset);
 
         static int preferences(const char *section, const char *name, int def);
         static float preferences(const char *section, const char *name, float def);
@@ -145,6 +141,7 @@ namespace XSwiftBus
             XPMPPlanePosition_t position;
             Plane(void *id_, QString callsign_, QString aircraftIcao_, QString airlineIcao_, QString livery_, QString modelName_);
         };
+
         QHash<QString, Plane *> m_planesByCallsign;
         QHash<void *, Plane *> m_planesById;
         qint64 m_timestampLastSimFrame = QDateTime::currentMSecsSinceEpoch();
@@ -154,8 +151,6 @@ namespace XSwiftBus
         {
             return static_cast<CTraffic *>(self)->getPlaneData(id, dataType, io_data);
         }
-
-        static int drawCallback(XPLMDrawingPhase phase, int isBefore, void *refcon);
     };
 }