Make useful_scripts run standalone with proper imports, path

This change enables scripts to run standalone and get all of their imports automagically as if they were run from `manage.py shell_plus`. Including `from setup_script import *` at the top of a standalone script allows us to write the rest of the script as if each line were typed at the shell, which is really useful.

I also magic-ified `finaid_approve.py` this way.