let the router handle dynamic files

[PF94]

the sb router already handles things like loading skin thumbnails and loading a file from the composer vendor folder through the load_thumbnail_from_skin() and load_file_from_vendor() functions, so I wonder why cant it also handle dynamic files (videos, profile pictures, thumbnails, etc)

PROS:

• hide private uploads
• hide uploads that require to be logged in from logged out users

CONS:

• adds overhead, would make the site a bit slower
• would fuck up with sb production instance's usage of nginx ratelimits.