Quick code for ban-checking

I haven't been able to test this yet because the tracker isn't handing out items but theoretically it should work.

Should cause the pipeline to not fetch an item if the users IP or the AT UA is banned.

I also noted that the UAs differ between the scripts so maybe the discover.py script could just be given a random UA like the main script (or even have it pass the random one as a parameter so that the ban check can still be done before fetching an item for that specific UA).