persist cookies to file, commands for working with groups

[neon-ninja]

Hi Chris!

Thanks for making this open source. Currently, garc will trigger a login each time it's run. If garc is run frequently, requests to https://gab.com/auth/sign_in can trigger Cloudflare's browser check, preventing the login. This commit will make it so that garc saves cookies after login to a file, in Netscape format. The file will be located adjacent to the config file (~/.garc by default), with the extension _cookies.txt (so ~/.garc_cookies.txt by default). The cookies file would then be used on the next run. As an added benefit, a user could use an extension like https://chrome.google.com/webstore/detail/get-cookiestxt/bgaddhkoddajcdgocldbbfleckgcbcid?hl=en to export their cookies from their browser and use those.

Take a look and let me know what you think

[neon-ninja]

https://github.com/stanfordio/gabber/pull/8 seems to have an alternative way of solving this

[neon-ninja]

PR amended to add commands for working with groups, hope you don't mind me bundling these features together