QmlCppEngine: StackWindow Behaviour

Enable/Disable the stack window based on engine state.
Update the markers in the stack window correctly.

Change-Id: Idbc694aa2a4be9497e2e3b2c9e9a1f463e1c7692
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>

src/plugins/debugger/stackhandler.h

@@ -85,6 +85,9 @@ public:
     void scheduleResetLocation();
     void resetLocation();
 
+signals:
+    void stackChanged();
+
 private:
     // QAbstractTableModel
     int rowCount(const QModelIndex &parent) const;