[ticket/13051] Fix viewonline event, remove template data

PHPBB3-13051
[ticket/13051] Add a new core event to handle the template array

PHPBB3-13051
[ticket/13051] Rename new event core.viewonline_modify_user_row

PHPBB3-13051
[ticket/13051] Fix core event name

PHPBB3-13051
Merge pull request #2934 from VSEphpbb/ticket/13051

[ticket/13051] Fix viewonline event (recently broken) and add a new core event