Add option to enable threading, with default to off.

bridge/config/config.go

@@ -99,6 +99,7 @@ type Protocol struct {
 	NoTLS                  bool       // mattermost
 	Password               string     // IRC,mattermost,XMPP,matrix
 	PrefixMessagesWithNick bool       // mattemost, slack
+	PreserveThreading      bool       // slack
 	Protocol               string     // all protocols
 	QuoteDisable           bool       // telegram
 	QuoteFormat            string     // telegram

gateway/gateway.go

@@ -263,7 +263,7 @@ func (gw *Gateway) handleMessage(msg config.Message, dest *bridge.Bridge) []*BrM
 
 	// Get the ID of the parent message in thread
 	var canonicalParentMsgID string
-	if msg.ParentID != "" {
+	if msg.ParentID != "" && (gw.Config.General.PreserveThreading || dest.GetBool("PreserveThreading")) {
 		thisParentMsgID := dest.Protocol + " " + msg.ParentID
 		canonicalParentMsgID = gw.FindCanonicalMsgID(thisParentMsgID)
 	}