[Complicated] [2.0] Allow using multiple logins both for ratelimits and filling holes

[Scripter17]

Ignoring sessions and tokens and pagination and all the other ways this won't ever work, it'd be neat if the average person could easily do what Kemono does with using multiple accounts to get more stuff

Unfortunately this'd require a near complete rewrite of any extractor that wants to use it, so it's best left for the ever-hypothetical gallery-dl 2.0