Attach scripts to output images

[awalter17]

When running a script which outputs an image it would be nice if the script used to create the image was attached to the output image.

For example, you have a script which inverts an image. Takes one image as input and produces one image as output. The image which is output should have the invert script attached to it. That way users know how it was created.

One thing to consider:

Say a script is used on many images, and then saved as a new file many times to the server (i.e. duplicate files get saved to the server, which eventually could take up a lot of space). We'd want to ensure that the script is only stored in the database once, and (if needed) referenced by many images.