Expert Configuration dialog was too slow when accessibility was used.
Therefore the table was changed to tree view. In tree view the children
of entries is loaded dynamically.

Change-Id: I267833e46005058fdfedb6f012afe2f9b390636b
Reviewed-on: https://gerrit.libreoffice.org/16307Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>