Vehicle: add roiCoordChanged signal:

this allows for ROI commanded elsewhere than clicking on map
( like gimbal panel point home action ) to show the ROI indicator
on map

src/Vehicle/Vehicle.cc

@@ -2892,6 +2892,8 @@ void Vehicle::guidedModeROI(const QGeoCoordinate& centerCoord)
                     static_cast<float>(centerCoord.longitude()),
                     static_cast<float>(centerCoord.altitude()));
     }
+    // This is picked by qml to display coordinate over map
+    emit roiCoordChanged(centerCoord);
 }
 
 void Vehicle::stopGuidedModeROI()

src/Vehicle/Vehicle.h

@@ -1021,6 +1021,7 @@ public slots:
     void mavlinkStatusChanged           ();
 
     void isROIEnabledChanged            ();
+    void roiCoordChanged                (const QGeoCoordinate& centerCoord);
     void initialConnectComplete         ();
 
     void sensorsParametersResetAck      (bool success);