Overhaul highlight system (#3399)

Checks have been moved into a Controller allowing for easier tests.

src/providers/twitch/IrcMessageHandler.cpp

@@ -264,6 +264,7 @@ void IrcMessageHandler::addMessage(Communi::IrcMessage *_message,
     MessageParseArgs args;
     if (isSub)
     {
+        args.isSubscriptionMessage = true;
         args.trimSubscriberUsername = true;
     }