CLI Authentication

[DominikWidomski]

Actually, store the auth file as .justinconfig or .justinrc and the location is not clear either, as it makes sense to me to store this only as a form of cache for the app (but not necessarily as expendable as some cache).

Want to move away from username/password as primary authentication method and instead use user generate persona access tokens, much like Github. This requires work in Justin API however at the moment.

In the mean time would like to support username/password with -u <username> -p options, then saving the auth token in the config file.