Use Scene3D plugin from ign-gui2 in visualizer2

The Scene3D plugin from ign-gui2 will make a service
request to get information about a scene, with the
service name configurable via xml. It expects
different data types than delphyne though, so
some more changes are needed.

delphyne_gui/visualizer/layout2_with_teleop.config

@@ -81,8 +81,14 @@
     </plugins>
   </menus>
 </window>
-<plugin filename="delphyne_gui_render_widget">
+<plugin filename="Scene3D">
+  <engine>ogre</engine>
+  <scene>scene</scene>
+  <service>/get_scene</service>
   <has_titlebar>false</has_titlebar>
+  <ambient_light>0 0 1</ambient_light>
+  <background_color>0.8 0.8 0.8</background_color>
+  <camera_pose>-6 0 6 0 0.5 0</camera_pose>
 </plugin>
 
 <plugin filename="WorldControl">