[ticket/9550] Add template event ucp_pm_viewmessage_custom_fields_before

Adds a template event required for the karma extension. It allows adding data
before the custom fields under the username and avatar next to every private
message in prosilver.

Explanation from http://area51.phpbb.com/phpBB/viewtopic.php?f=111&t=44379:
Used by the karma extension to add a karma score indication that allows users
to see how respected the pm sender is.

PHPBB3-9550
[ticket/9550] Add template event ucp_pm_viewmessage_custom_fields_after

Adds the append counterpart of a template event required for the karma
extension. It allows adding data after the custom fields under the username
and avatar next to every private message in prosilver.

Explanation from http://area51.phpbb.com/phpBB/viewtopic.php?f=111&t=44379:
Per suggestion of nickvergessen, add a counterpart for every append or prepend
event.

PHPBB3-9550
[ticket/9550] Add template event memberlist_body_username_append

Adds a template event required for the karma extension. It allows adding
information after every username in the memberlist.

Explanation from http://area51.phpbb.com/phpBB/viewtopic.php?f=111&t=44379:
Used by the karma extension to add a karma score indication that allows other
users to see how respected every listed user is.

PHPBB3-9550
[ticket/9550] Add template event memberlist_body_username_prepend

Adds the prepend counterpart of a template event required for the karma
extension. It allows adding information before every username in the
memberlist.

Explanation from http://area51.phpbb.com/phpBB/viewtopic.php?f=111&t=44379:
Per suggestion of nickvergessen, add a counterpart for every append or prepend
event.

PHPBB3-9550
[ticket/9550] Add the new template events to phpBB/docs/events.md

The newly added template events weren't listed and described yet in events.md.
Fixed now.

PHPBB3-9550