Remove the segmentation of the NIST files

The segmentation is removed at this moment of the upload process. The
retrieval of the images will be done later on when we need the image. A
thumbnails could be saved while the image is generated for the user (or
by a background task) later on (feature not available at the moment).

This approach will facilitate the work with NIST files later on: instead
of trying to process the file at the upload, we will implement the
feature later on. This will imply that ICNML would be, for a moment,
capable of storing NIST files but not working or displaying them.