Fixed authentication using Linkedin

Fixed authentication using Linkedin as reported in https://github.com/gae-init/gae-init-auth/issues/34 based on example code provided at https://github.com/lepture/flask-oauthlib/blob/master/example/linkedin.py (though some further simplifications could be made based on existing code...)
`full_name` is used twice... for `name` and `username`, but I will do something in this spirit...