Draft: Provide custom Session wrapper with default token_scope

This MR introduces a new gwdatafind.Session object as a thin wrapper around igwn_auth_utils.Session with the token_scope defaulting to 'gwdatafind.read'.

This MR then updates the underlying get() calls in gwdatafind.ui to use the new Session wrapper, which, when combined with requiring igwn-auth-utils-1.0.0, simplifies the request handling (all of the work is now done by igwn-auth-utils.