Ref T775, special handling for "broadcast" messages

* identify broadcast messages
* do NOT play sound
* use "own" tab for text messages (group together)

src/blackmisc/network/textmessage.h

@@ -114,6 +114,9 @@ namespace BlackMisc
             //! Initial message of server?
             bool isServerMessage() const;
 
+            //! Is this a broadcast message
+            bool isBroadcastMessage() const;
+
             //! Whole message as formatted string. Used to display message in a console window.
             //! \param withSender        include sender information in string?
             //! \param withRecipient     include recipient information in string?
@@ -156,6 +159,9 @@ namespace BlackMisc
             //! Mark as relayed message
             void markAsRelayedMessage() { m_relayedMessage = true; }
 
+            //! Mark as broadcast message
+            void markAsBroadcastMessage();
+
             //! Mark as relayed and keep original sender
             void makeRelayedMessage(const Aviation::CCallsign &partnerCallsign);