QmlDesigner: Show context menu in the states editor in whole view

Change-Id: I656c803f066bcdf1b3b39879194cc4698832083b
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
QmlDesigner: Use Rectangle instead of Item for dummy Window

Task-number: QTCREATORBUG-12484
Change-Id: I6d96367159dd813531046af4412bc10e5cb5df0f
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>