QmlDebug: Parse application output to track debugees state

Setting up the debugger connection might fail for a couple of reasons.
Check the application output to show the user a more detailed error
message.

Reviewed-by: hjk

src/plugins/debugger/qml/qmlengine.h

@@ -61,10 +61,17 @@ public:
     void gotoLocation(const Location &location);
     bool canDisplayTooltip() const;
 
+    void showMessage(const QString &msg, int channel = LogDebug,
+                     int timeout = -1) const;
+    void filterApplicationMessage(const QString &msg, int channel);
+
 public slots:
     void messageReceived(const QByteArray &message);
     void disconnected();
 
+private slots:
+    void messageBoxFinished(int result);
+
 private:
     // DebuggerEngine implementation.
     bool isSynchronous() const { return false; }