Change toolbox startup mechanism

This prevents problems with toolbox references from inside
QGCTool::setToolbox calls.

src/QGCApplication.cc

@@ -343,6 +343,7 @@ QGCApplication::QGCApplication(int &argc, char* argv[], bool unitTesting)
     initializeVideoStreaming(argc, argv);
 
     _toolbox = new QGCToolbox(this);
+    _toolbox->setChildToolboxes();
 }
 
 QGCApplication::~QGCApplication()

src/QGCToolbox.cc

@@ -71,7 +71,10 @@ QGCToolbox::QGCToolbox(QGCApplication* app)
     _qgcPositionManager =       new QGCPositionManager(app);
     _followMe =                 new FollowMe(app);
     _videoManager =             new VideoManager(app);
+}
 
+void QGCToolbox::setChildToolboxes(void)
+{
     _audioOutput->setToolbox(this);
     _autopilotPluginManager->setToolbox(this);
     _factSystem->setToolbox(this);

src/QGCToolbox.h

@@ -61,6 +61,8 @@ public:
 #endif
 
 private:
+    void setChildToolboxes(void);
+
     GAudioOutput*               _audioOutput;
     AutoPilotPluginManager*     _autopilotPluginManager;
     FactSystem*                 _factSystem;
@@ -81,6 +83,8 @@ private:
     FollowMe*                   _followMe;
     QGCPositionManager*         _qgcPositionManager;
     VideoManager*               _videoManager;
+
+    friend class QGCApplication;
 };
 
 /// This is the base class for all tools