feature: prevent duplicated files
feature: prevent duplicated files

- If the user uploads a file that already exists under their account, it will return the previous url
- If an anonymous user uploads a file and already exists previously from another anon, return that url
- Files are unique per account since they can be deleted, anonymous files can't

WeebDev/loli-safe,WeebDev/loli-safe,WeebDev/lolisafe,WeebDev/lolisafe