Merge branch '5.2'

diff --cc files/lib/data/conversation/ConversationAction.class.php
index 9a1dec18c1573cbab8d1efd29bbaf68d0a0f7f22,898401ded1a2a06a1d0891d41b1c4ef28a61df9b..c7d8f595c7ea1d51f25e6df2afd4262dd93a946e
--- 1/files/lib/data/conversation/ConversationAction.class.php
--- 2/files/lib/data/conversation/ConversationAction.class.php
+++ b/files/lib/data/conversation/ConversationAction.class.php
@@@ -6,8 -6,8 +6,9 @@@ use wcf\data\conversation\message\Conve
  use wcf\data\conversation\message\SimplifiedViewableConversationMessageList;
  use wcf\data\AbstractDatabaseObjectAction;
  use wcf\data\IClipboardAction;
 +use wcf\data\IPopoverAction;
  use wcf\data\IVisitableObjectAction;
+ use wcf\data\user\group\UserGroup;
  use wcf\system\clipboard\ClipboardHandler;
  use wcf\system\conversation\ConversationHandler;
  use wcf\system\database\util\PreparedStatementConditionBuilder;