Fix Slider regression

The change in implicit size means that by default the size is not
0. Since the slider was creating a hidden slider item, we have to
hide this explicitly.

Change-Id: I5342376ab209409a580b9380deff6f53b0d94f63
Reviewed-by: Daker Fernandes Pinheiro <daker.pinheiro@openbossa.org>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@nokia.com>

components/Slider.qml

@@ -54,6 +54,7 @@ Components.Slider{
         elementType: "slider"
         contentWidth:23
         contentHeight:23
+        visible: false
     }
 
     property int orientation: Qt.Horizontal