[ticket/15735] Add viewtopic_body_postrow_content_after template event

Needed for extensions who adds information at the end of the message
(such as moderator messages).

PHPBB3-15735

phpBB/styles/prosilver/template/viewtopic_body.html

@@ -326,6 +326,8 @@
 
 			<div class="content">{postrow.MESSAGE}</div>
 
+			<!-- EVENT viewtopic_body_postrow_content_after -->
+
 			<!-- IF postrow.S_HAS_ATTACHMENTS -->
 				<dl class="attachbox">
 					<dt>