[ticket/13050] Allow topic/forum subscription when email/jabber is off

Currently, there's impossible to subscribe topic/forum if emails and/or jabber
is disabled. This seems to be a 3.0 leftover since 3.1 introduces new
notification system which handles this case and offers email/jabber-free
board notifications.

PHPBB3-13050
[ticket/13026] Add template vars array to core.viewonline_overwrite_location

Add template vars array to core.viewonline_overwrite_location event
to allow modifying/adding template vars for every user row.

PHPBB3-13026
[ticket/13020] Add forum_data variable to core.viewforum_get_topic_data event

PHPBB3-13020
Merge pull request #2911 from rxu/ticket/13020

[ticket/13020] Add variables to core.viewforum_get_topic_data event
Merge pull request #2915 from rxu/ticket/13026

[ticket/13026] Add template vars array to core.viewonline_overwrite_location
Merge pull request #2931 from rxu/ticket/13050

[ticket/13050] Allow topic/forum subscription when email/jabber is off

* rxu/ticket/13050:
  [ticket/13050] Allow topic/forum subscription when email/jabber is off