Add code in DOCX importer to handle 'table cell redline'

Change-Id: Ic1e2cb1873dc696311382108868abc4aee00baef
Reviewed-on: https://gerrit.libreoffice.org/7872
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>