add support to select camera track target by clicking in the scene browser
add support to select camera track target by clicking in the scene browser

fixes #402

openhumanoids/director,mitdrc/director,manuelli/director,patmarion/director,patmarion/director,manuelli/director,manuelli/director,mitdrc/director,mitdrc/director,mitdrc/director,patmarion/director,mitdrc/director,patmarion/director,openhumanoids/director,openhumanoids/director,manuelli/director,manuelli/director,patmarion/director,openhumanoids/director,openhumanoids/director