Short introduction to this demo
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What do we want to achieve?

o display the images of the 4 detectors of NIRMOS separated by a bar
o attach/detach to image events for all 4 detectors
o apply cut level settings, scale factor, etc. for either a selected
  image or for all 4 images
o panning of all images in a separate window

How to do it with RTD

o Create a standard directory 'rtdq4'
o Create a tcl script rtdq4.tcl which
  - does a 'package require' of Rtd
  - starts the application
o copy the Rtd demo application from /vlt/dflow/lib/rtd/Rtd.tcl
  (for some applications it may be easier to inherit this class)
  - in method init which is called from the base class (TopLevelWidget)
    after all options have been evaluated, change the layout:
    - the menu bar and menu items
    - the control and image frame
    - the 4 RTD images packed into the image frame
    - the horizontal and vertical bar to separate the images
    - the control functions for zoom, cut, pixel value display at
      cursor position, ...
  - some of the methods were taken from RtdImageCtrl.tcl
o modify the methods which deal with all 4 images like
  - set_cut_levels
  - attach_camera, detach_camera
  - updateValues
o since the Rtd demo application only works for one image some
  methods of some classes had to be redefined:
  - RtdImageTrans::fill_mag_menu      sets the scale for all windows
  - RtdImageZoomView::enter_image     sets the target image for zooming