No ratelimit on skin upload

It would appear that there's no limit on file upload speed via the upload skin system. This allows for a theoretical resource exhaustion attack, though I'd imagine Mojang's servers have quite a bit of file storage. However, this is still an issue and could be easily fixed by implementing something like a 1 minute timeout after 5 skins have been uploaded. It could be that something like this already exists, but I've uploaded 30-40 files in the last few minutes and haven't hit a ceiling yet.