QmlDesigner.MetaInfo: fix meta system for Qt enums

Change-Id: I87bedb03998d281d4a6bd450cb58d4614ae19187
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlDesigner.MetaInfo: fix for propertyCastedValue

Using convert() had the side effect of invalidating the variant.

Change-Id: Iebfbf6a8067343c7c1436d6dec5ef8090821ed33
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlDesigner.MetaInfo: fixing isLayoutable()

The major version is the version of the layout.
QtQuick.Layots have version 1.0.

Change-Id: Id83105ab858a74563e8ea6457d91613d20514fcb
Reviewed-by: Marco Bubke <marco.bubke@digia.com>