Added two new writer commands: NextTrackedChange (FN_REDLINE_NEXT_CHANGE) and
 PreviousTrackedChange (FN_REDLINE_PREV_CHANGE).
Rewrote the logic for Accept/Reject change (FN_REDLINE_ACCEPT_DIRECT and
 FN_REDLINE_REJECT_DIRECT) to work well with the newly introduced commands.

Change-Id: I03d583bef4225409f69934f16db1854564c2db5f
Reviewed-on: https://gerrit.libreoffice.org/1156Reviewed-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>
Tested-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>