Allow ripping from sites that require username/password

[4pr0n]

Examples: Facebook, Twitter, Instagram, Tumblr

These sites have some content that's only accessible from specific accounts.

[4pr0n]

1. Check if album is publicly visible; if not, ask for username/password in a pop-up window
2. Login, save cookies.
3. Rip normally.

Most sites use OAuth2 for authentication which would be a pain point.

[Phenrei]

A suggestion regarding this that I've seen done by an expensive paid ripper (it would likely also fix the issues with sites you can't log in to like flickr): import the active cookies from the browser when downloading from sites. I believe Firefox would require just sqlite to do this reading, though the ripper I saw used all 4 major browsers.

[Doleman]

Furaffinity and Hentai-Foundry I've found don't save all the images even after the suggestion made about saving the cookie. It's a strange case because for some users it'll download all the images while for others it won't. I think it has something to do with Furaffinity's option to switch between Safe for Work and Not Safe for Work. for comparrison: lionalliance will have all of their images download even the NSFW ones (over 400 images) While giantgrowingvixen will only download 17, (when the user has over 120 images)

[Phenrei]

It's actually a secondary problem I coded a fix for that's pending (https://github.com/4pr0n/ripme/pull/100). Those sites support multiple image formats for files and the ripper currently assumes they're all .jpg because it doesn't go to the image page to check (like it does for some rippers) and doesn't support a check/fallback for this. Per-page checking is probably safer, but a file format fallback feature was faster to rip and less likely to get some part of the ripper banned from hitting the site too hard.