first commit

1. load file list from image directory (published input:
Image_directory)
2. user random number generator to select two images from the directory
at alternating intervals (published input: Image_duration_seconds)
3. limit image sizes if their dimensions exceed a specified value
(first image at maximum 100% height of the rendering destination
dimensions, second image at 150% the height of the rendering
destination)
4. display the images (the first image in the centre of the left side
of the rendering destination, the second image in the bottom centre of
the right side of the image)