Do not autologin with webbrowser.open.

When running `jupyter notebook`, this will automatically login users, thus preventing them to see the login page allowing them to set a password.

I suggest to change the flow so that on startup it does not pass `?token=...` but `?prefill_token=...`, stop users on above page by pre-filling the token, and let users set-up a password.

Start with the startup flow for `jupyter notebook`, particularly the path that calls `webbrowser.open` and adds the token query parameter. Trace how the login page handles that parameter; done means startup uses `prefill_token` instead of `token`, allowing users to reach the page and set a password.

Written by the indexing model from the issue text.