Improve usability of the outline

If you had data in the outline and would scroll to the bottom then it would be
an empty view at the bottom. The width of the outline was defined as a fixed
with twice. Once in the outlnvsh and one (even smaller) in the outlview. I have
changed the with of the outlview to take the with of the outlnvsh.

Change-Id: I1376a135acd92dbe8966b29ccb075e6b74412a8c
Reviewed-on: https://gerrit.libreoffice.org/7832
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>