At the request of Aleeri in group, add support for EXP-901

Notifies nonfriends when their chat is blocked
This is instead of showing the muted autoresponse message, so only muted people will see it now.

Also cleans up some excess autoresponder code.

indra/newview/llimview.cpp

@@ -1086,6 +1086,16 @@ LLFloaterIMPanel* LLIMMgr::createFloater(
 	return floater;
 }
 
+void LLIMMgr::addNotifiedNonFriendSessionID(const LLUUID& session_id)
+{
+	mNotifiedNonFriendSessions.insert(session_id);
+}
+
+bool LLIMMgr::isNonFriendSessionNotified(const LLUUID& session_id)
+{
+	return mNotifiedNonFriendSessions.end() != mNotifiedNonFriendSessions.find(session_id);
+}
+
 void LLIMMgr::noteOfflineUsers(
 	LLFloaterIMPanel* floater,
 	const LLDynamicArray<LLUUID>& ids)