feat(plex user auth): Use the built in plex user auth instead of server token

[soehlert]

This allows for a few really nice things:

1. you don't have your server token floating around (still don't love your password has to live in a file on disk somewhere - but thats outside the scope of this)
2. any server your account has access to, you can use with tunebox
3. this includes remote servers
4. this sets us up to maybe make that on the fly configurable!