Fix QDeclarativeListProperty assignment

Fix QDeclarativeListProperty assignment

This commit ensures that a QDeclarativeListReference can be
assigned to another QDeclarativeListProperty, by retrieving
each element in the list reference and converting to the appropriate
type before appending to the target list property.

Task-number: QTBUG-16316
Change-Id: Id8858058f052a53bf43eadc085fd278654478d77
Reviewed-on: http://codereview.qt-project.org/4388
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Aaron Kennedy <aaron.kennedy@nokia.com>