[ticket/11566] add interface for captcha

PHPBB3-11566
[ticket/11566] add error functionality

PHPBB3-11566
[ticket/11566] add error in template

PHPBB3-11566
[ticket/11566] display error instead of trigger_error

PHPBB3-11566
[ticket/11566] add captcha reset and hidden fields

PHPBB3-11566