added a script for making booster packs.

It's just a dinky little python script, that currently just creates some new folders and randomly copies images into each one. There's some support for different card rarities too.

Possible future work includes using the Pillow library to stitch together card images into a single A4/Letter for printing, so you can do a physical booster draft.

The script doesn't do anything a python novice couldn't follow (after all, I am one), but there's a readme file in the zip that tells you how to configure it even if you don't know any python.