QmlDesigner.PropertyEditor: adding missing qsTr()

Change-Id: Ifcda7118cce9858af4670d60d902868c9e45e90a
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
QmlDesigner.PropertyEditor: fixing text label in LayoutSection

Change-Id: Ia0a065da9f24de81147a9ae7d939654e24f0862c
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>