[feature/oauth] Login_link register form

PHPBB3-11673
[feature/oauth] Start working on login_link registration support

PHPBB3-11673
[feature/oauth] Login_link in registration

PHPBB3-11673
[feature/oauth] Fix errors on ucp_login_link

PHPBB3-11673
[feature/oauth] Login_link works with ucp_register now

PHPBB3-11673