[feature/oauth] Error handling on page

PHPBB3-11673
[feature/oauth] Build OAuth data for ucp_auth_link

PHPBB3-11673
[feature/oauth] Get the OAuth template in place for ucp_auth_link

PHPBB3-11673
[feature/oauth] Handle hidden fields

PHPBB3-11673
[feature/oauth] Start implementing link/unlink actions

PHPBB3-11673
[feature/oauth] Fix errors in ucp_auth_link

PHPBB3-11673
[feature/oauth] Update link_account to allow for two methods of linking

PHPBB3-11673
[feature/oauth] Refactor oauth::link_account for two paths

PHPBB3-11673
[feature/oauth] Fix errors found in testing linking

PHPBB3-11673
[feature/oauth] Document internal functions

PHPBB3-11673
[feature/oauth] Add unlink_account to auth interface

PHPBB3-11673
[feature/oauth] Implement unlinking in OAuth

PHPBB3-11673
[feature/oauth] Fix errors in oauth

PHPBB3-11673