bnc#897769: OOXML import: Import border lines using reference too.

Do not ignore 'lnRef' element.

Also fix typo to apply 'seCell' properties to the right cell (southeast).

Change-Id: Ia45f7016f358b70e6db06a232c569335ce9d7051
(cherry picked from commit 18898e13fda25fe6dc85318dd0711355c7b2cc26)
Reviewed-on: https://gerrit.libreoffice.org/11652
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>