QmlDesigner: move ScrollViewStyle to common directory

Change-Id: Ieb235aab921bd5d246403ff42b4659090c8abdbf
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlDesigner: cleanup unused methods

 - remove javascript methods: scrollView(delta), resetView()
 - remove javascript related signals
 - remove visibleCount debug output

Change-Id: I63b0a204d7f570986e41fc9fb3762f13e5d63d79
Reviewed-by: Marco Bubke <marco.bubke@digia.com>