QmlProfiler: Consistently clear when clear button pressed

Several QML properties need extra treatment to avoid stale data
after clearing. Toggling the visibility of the timeline renderer
doesn't really help there.

Task-number: QTCREATORBUG-11833

Change-Id: I1903d7bd69d6fe31ecc4cadca8e30fa2104fa09a
Reviewed-by: Christian Stenger <christian.stenger@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>

src/plugins/qmlprofiler/qml/Overview.qml

@@ -43,7 +43,7 @@ Canvas {
     property real endTime : 0
 
     // ***** functions
-    function clearDisplay()
+    function clear()
     {
         dataReady = false;
         requestPaint();