Fix ignoring closeEvents on OSX for QtQuick.

The QCloseEvent's accepted state should not be inverted for the
QWindowSystemInterfacePrivate::CloseEvent. To make Widgets work
with this change, pass whether the close was accepted from close_helper
to the QCloseEvent generated by QGuiApplication.

Task-number: QTBUG-28965

Change-Id: If384b0355776b93df02dff2ab78b5647903200e7
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Reviewed-by: Josh Faust <jfaust@suitabletech.com>