Add parent and child functions to QAccessibleInterface.

Add parent and child functions to QAccessibleInterface.

Stop the mis-use of navigate to find the parent.
In order to make navigation straight forward
parent and child functions are now part of
QAccessibleInterface.
This allows navigating the hierarchy of
accessible objects without the 1-based indexes in the
navigate function which lead to confusion.

Eventually the support for Ancestor in navigate can be completely removed
and forwarded in the windows bridge if needed.

In addition default parameters for virtual children.
This will make the transition smooth since it allows to remove the integer
already.

Change-Id: I278287ce17161f9fa46797ac244676778c859576
Reviewed-on: http://codereview.qt-project.org/5024
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@nokia.com>
Reviewed-by: Jan-Arve Sæther <jan-arve.saether@nokia.com>