QmlObserver: Add 'show app on top' switch to creator + qmlobserver

This is convenient especially in the observer mode.

Reviewed-by: Christiaan Janssen

share/qtcreator/qml/qmljsdebugger/qdeclarativeviewobserver_p.h

@@ -83,6 +83,7 @@ public:
     BoundingRectHighlighter *boundingRectHighlighter;
 
     bool designModeBehavior;
+    bool showAppOnTop;
 
     bool executionPaused;
     qreal slowdownFactor;