StatechartViewer: multiple statecharts can be tracked

.../gui-plugins/StatechartViewerPlugin/IceStateConverter.cpp

...ui/gui-plugins/StatechartViewerPlugin/IceStateConverter.h

...rXGui/gui-plugins/StatechartViewerPlugin/StateWatcher.cpp

...ins/StatechartViewerPlugin/StatechartViewerController.cpp

...ugins/StatechartViewerPlugin/StatechartViewerController.h

...StatechartViewerPlugin/controller/ActiveStateFollower.cpp

...s/StatechartViewerPlugin/controller/ActiveStateFollower.h

...ui-plugins/StatechartViewerPlugin/layout/LayoutWorker.cpp

...ui-plugins/StatechartViewerPlugin/view/StateTabWidget.cpp

...ui-plugins/StatechartViewerPlugin/view/StatechartView.cpp

...i-plugins/StatechartViewerPlugin/view/StatechartViewer.ui