WebAccess: Automatically fetch nicknames from SSO

* Automatically updates the nickname for extarnal
  authenticated users.

Co-authored-by: Nikolaos Kasioumis <nikolaos.kasioumis@cern.ch>
Signed-off-by: Harris Tzovanakis <me@drjova.com>
Merge pull request #81 from drjova/webaccess-sso

WebAccess: Automatically fetch nicknames from SSO