Added auto rotate pan

[khairu-aqsara]

based on this issues https://github.com/googlevr/vrview/issues/34 added image automatically starts to rotate like this: http://photo-sphere-viewer.js.org/ if is_autopan_off is set to false with default speed 20000 and the rotation speed can be set up using auto_pan_speed

  vrView = new VRView.Player('#vrview', {
    width: '100%',
    height: 480,
    image: 'blank.png',
    is_stereo: false,
    is_autopan_off: false,
    auto_pan_speed:xxxxx
  });