Use sorted image list in toolbox.py

[gcroonen]

I noticed in toolbox.py (used by for instance object_detection.py) the files are processed in order the OS presents them in. This can cause a lot of confusion when viewing and comparing the output images. I think it would better to process the files in sorted order.

Changing this from line 588 onwards:

        images = [
            read_rgb(img)
            for img in path.glob("*")
            if img.suffix.lower() in IMAGE_EXTENSIONS
        ]

To this:

        images = [
            read_rgb(img)
            for img in sorted(path.glob("*"))
            if img.suffix.lower() in IMAGE_EXTENSIONS
        ]

Solves this problem.