Add derived class 'SwTableRowRedline' stub

Add stub derived class 'SwTableRowRedline' that will hold information
about the table row that got the changes, including the actual change
that was done (inserted\deleted).

Change-Id: I8b6ef9da3f3d9859a1e908dbcc018bc5c54b8329
Reviewed-on: https://gerrit.libreoffice.org/7466
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>