Ref T761, partner callsign message relay (swift with co-pilot)

* handle server error messages correctly as "error"
* (relayed) sender can be ATC or aircraft
* relay private messages correctly

src/blackmisc/network/textmessage.cpp

@@ -97,7 +97,7 @@ namespace BlackMisc
             if (index < CTextMessage::swiftRelayMessage().length()) { return false; }
             if (m_message.length() <= index + 1) { return false; } // no next line
             const QString originalSender = m_message.left(index).remove(CTextMessage::swiftRelayMessage()).trimmed();
-            this->setSenderCallsign(CCallsign(originalSender, CCallsign::Aircraft));
+            this->setSenderCallsign(CCallsign(originalSender)); // sender can be aircraft or ATC
             m_message = m_message.mid(index + 1);
             return true;
         }

src/blackmisc/network/textmessagelist.cpp

@@ -109,6 +109,7 @@ namespace BlackMisc
             int c = 0;
             for (CTextMessage &m : *this)
             {
+                // Turn "relay" message into private message
                 if (m.relayedMessageToPrivateMessage()) { c++; }
             }
             return c;