QmlProfiler: Reimplement zoom slider in QML

This restores the functionality of the old zoom slider. It probably
looks a bit different, but it does the same thing.

Task-number: QTCREATORBUG-10635

Change-Id: Idcb19187df066e4b1336df73b122aa567a732dee
Reviewed-by: Kai Koehne <kai.koehne@digia.com>

src/plugins/qmlprofiler/qmlprofilertraceview.h

@@ -137,6 +137,7 @@ signals:
     void lockModeChanged(bool);
     void enableToolbar(bool);
     void zoomLevelChanged(int);
+    void showZoomSlider(bool);
 
     void resized();