Auth changes

[sameeraja bns]

Hi,

For multiple atsigns some changes have been made in auth methods. Now the "namespace" is included in atClientPreference itself. Please refer  https://github.com/atsign-company/at_settings/blob/dev_env/lib/services/at_me_service.dart for "authenticate" and "onboard" method changes. Multiple atsigns - ui and server changes  are in dev_env and will get published to pub_dev by monday.

Thanks and Regards,

Sameeraja