Fix Beware's issue with SinguReplaceLinks failing for system messages

Fixes Teleport Offers in local being links
Fixes System Messages in IMs not enforcing link replacement
Fixes IM Chat History being loaded with replacement support,
at the log point, we can only consider it text from an outside source.
Changes IM Chat History color from hard coded grey to SystemChatColor

indra/newview/llagent.cpp

@@ -4973,6 +4973,7 @@ void LLAgent::onFoundLureDestination(LLSimInfo *siminfo)
 			msg.append(llformat(" (%s)", maturity.c_str()));
 		}
 		LLChat chat(msg);
+		chat.mSourceType = CHAT_SOURCE_SYSTEM;
 		LLFloaterChat::addChat(chat);
 	}
 	else