Script to scrub non-whitelisted tags from metadata

I think I got the sha calculation correct, but it'd be good for someone to double-check it.

I set up a dummy server and ran the script, testing that the resulting data was missing non-whitelisted tags

We have an amazing wealth of tags existing, but I guess they're all going to go away: https://gist.github.com/alastair/ac2484e773267226bb1b#file-x-alltags