DOCX Export of 'Table Cell Redline' (like insert cell or delete cell)

This patch adds support in the DOCX exporter for exporting the
'table cell redlines', such as 'inserted a table cell',
or 'removed a table cell'.

Change-Id: Ic37d2550691f1090a580dae57d597c8fd09c7ad9
Reviewed-on: https://gerrit.libreoffice.org/7877
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>