Black out polygons on images

[manthey]

This is a summary of what we talked about. For any given file, we probably want to do the following:

• If the file isn't already a tiff file, use large_image_converter to convert it to our preferred format. We might want to do this in all cases initially for a simple code path.
• For each tiles or associated image that needs to have an area be redacted, open the image with vips, draw a filled polygon in the appropriate spot, and save that image. Vips tends to only work with a single size image, so this probably needs to be run for each image that needs redaction. For tiled images, we want to output tiled images with the same parameters that large_image_converter would have chosen. For associated images, these should be in the same compression format as the originals. Note that all outputs are tiff files.
• Combine tiff files output from the previous step with portions of the original tiff file into a single output file. This can be done with tifftools. See large_image_converter for examples.

[manthey]

@mcovalt I've written how I would approach this.