fdo#86738 add links.txt references to next and previous buttons

Change-Id: I04514498e9f6466416d08eb0e1736dcebe931e71
Reviewed-on: https://gerrit.libreoffice.org/13186
Reviewed-by: Yousuf Philips <philipz85@hotmail.com>
Tested-by: Yousuf Philips <philipz85@hotmail.com>
(cherry picked from commit 401b7c8d7f0d46094e8bab7db9b2df8c74c5b876)
Reviewed-on: https://gerrit.libreoffice.org/13236