This patch adds support for 'Table Cell Redlines' (such as 'table cell inserted'
or 'table cell deleted' in SW core).
It adds the 'SwTableCellRedline' object, and adds a function for adding
objects of that type to the 'SwExtraRedlineTbl', which is the object
that holds all the redlines which are not 'Ranged' redlines.

Change-Id: Ic2e410be58683f171ea07d430b7544600780711e
Reviewed-on: https://gerrit.libreoffice.org/7873Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>