Switch to using NativeAuthenticator as default

[yuvipanda]

@leportella has been working on the awesome http:/jupyterhub/nativeauthenticator/. We should switch to using that as the default authenticator here rather than FirstUseAuthenticator.

Tasks

• Install nativeauthenticator by default
• Write docs on how NativeAuthenticator works
• Try find a way to seamlessly import FirstUseAuthenticator credentials into NativeAuthenticator - makes upgrades seamless for users.
• Switch to nativeauthenticator by default

Tasks added by Erik

• Expand the documentation for nativeauthenticator a bit, because it is our default authenticator.
  • Mention/Examplify the possibility of 2FA
  • Resolve NativeAuthenticator: Change password / Authorize links missing in top navigation bar at /hub/home UI #571

[consideRatio]

I'd love to help this go all the way, I'm a huge fan of the NativeAuthenticator!

@lambdaTotoro has recently cut version 1.0.5 of it, but we also need to address jupyterhub/nativeauthenticator#157 first I think.

@yuvipanda do you have something additional to say about this at this point in time?

[lambdaTotoro]

Having NativeAuthenticator be the default would be an honour! :D
But I'd definitely need some help on the fronts of interfacing with JupyterHub and docker/kubernetes/all of that jazz, because I'm not very experienced yet on either side.

[mtav]

• Expand the documentation for nativeauthenticator a bit, because it is our default authenticator.

Maybe this could even be done before switching to NativeAuthenticator by default. I certainly could have used it this week!
See here for more details.

I would suggest not only documenting specifically NativeAuthenticator configuration, but also how to properly set lists with tljh-config (in doc or in tljh-config -h), i.e. properly go from python code in other authenticator's documentations to tljh-config commands.
Or just directly document how to do it jupyterhub_config.d ?

See also #709 and #549 about tljh-config for lists/dicts/tuples.