Added QAccessibleGroupBox

Added QAccessibleGroupBox

Added a new accessible interface for QGroupBox, as QAccessibleDisplay
is not good enough when the QGroupBox is checkable.
AccessibleFactory was modified to return a QAccessibleGroupBox when
the accessible interface of a QGroupBox is requested.

Created tst_QAccessibility::groupBoxTest

Port to Qt5 of the patch by José Millán Soto <fid@gpul.org>

Change-Id: I6c23dcf5562b3ea269b04102e78463b65827188a
Reviewed-by: Jan-Arve Sæther <jan-arve.saether@nokia.com>
(cherry picked from commit c03ceb203c65d9e3485fad848bfc0c4b6ee3e9aa)