Support cookie-jar manipulation

[hannahwhy]

On Reddit, there are many subreddits that have an age gate. Clicking "Yes" sets an "over18=1" cookie for reddit.com. ArchiveBot cannot currently click buttons (even in PhantomJS mode), and so is blocked from archiving any subreddits that have age gates.

Reddit is not the only site that does this; other sites have similar cookie-based checks. We should be able to specify cookies up front. Perhaps a syntax like this:

!a http://cookies.example.com/ --cookie=.example.com:foo=1

which would add a nonsecure cookie with value foo=1 for .example.com.

More extensive customization is possible:

!a http://cookies.example.com/ --cookie-jar=https://gist.github.com/abcdefgh

This would download a cookie jar file from https://gist.github.com/abcdefgh and pass it to wpull. It is expected that the cookie jar would be usable by wpull.

[hannahwhy]

Another possibility, one that's less flexible but probably more useful, is to roll this into a more general site-specific customizations framework that's triggered on demand for given sites:

!a http://www.reddit.com/r/oculusnsfw/ --site-specific-settings  # or --sss I guess

(obviously, that link is NSFW)

This would also be a way to address #80.

[hannahwhy]

The immediate use case has been solved by https://github.com/ArchiveTeam/ArchiveBot/tree/reddit-over18.

[chfoo]

Just some ideas for on-the-fly commands:

• !cookie ident add|delete cookie-value-here: add/remove a cookie value
• !cookie ident flush: delete all cookies
• !cookie ident dump: print out the cookie jar