[ticket/9550] Add template event memberlist_view_user_statistics_before

Adds a template event required for the karma extension. It allows adding
entries to the user statistics part of any user profile.

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 this user is. Prepend because karma score is often
a more meaningful statistic than the bottom statistics (like "Most active
topic"), and should therefore be more prominent.

PHPBB3-9550

phpBB/styles/prosilver/template/memberlist_view.html

@@ -77,6 +77,7 @@
 	<div class="column2">
 		<h3>{L_USER_FORUM}</h3>
 		<dl class="details">
+			<!-- EVENT memberlist_view_user_statistics_before -->
 			<dt>{L_JOINED}{L_COLON}</dt> <dd>{JOINED}</dd>
 			<dt>{L_VISITED}{L_COLON}</dt> <dd>{VISITED}</dd>
 			<!-- IF S_WARNINGS -->

phpBB/styles/subsilver2/template/memberlist_view.html

@@ -66,6 +66,7 @@
 		</td>
 		<td class="row1">
 			<table width="100%" cellspacing="1" cellpadding="2" border="0">
+			<!-- EVENT memberlist_view_user_statistics_before -->
 			<tr>
 				<td class="gen" align="{S_CONTENT_FLOW_END}" nowrap="nowrap">{L_JOINED}{L_COLON} </td>
 				<td width="100%"><b class="gen">{JOINED}</b></td>