[camera] create new scene for each camera

fix #371
[builder] add basics after creating scenes
[builder] name new scenes
[builder] add comment camera-scene in env.create
[camera] update objects' pose/orientation

on the scene. introduce a new wierd stuff :-)
[camera] add scene as underlay (not shown)
[test] update video_camera pgm images
[camera] set viewport to camera
[builder] do not create scene for external robot