Save vertical space by putting labels and checkboxes in the same row…

... as dialog buttons.

Change-Id: Ieea882b467c87093e7648590bbf14fe6dfa0b7ee
Reviewed-on: https://gerrit.libreoffice.org/13061
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>