Fix the new_pull_request method from the internal API to use the new user model

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>
Fix the is_repo_admin method to use the new user model

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>
Fix link in the forks template to use the new user model

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>
Fix link in the requests template to use the new user model

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>