Did some changes inspired by Noel, corrected the
transformation due to mirroring already applied,
re-added 'mirror this window back'-mode

Change-Id: I21999e59898cf672fd293bc2b11f5d568e6673be
Reviewed-on: https://gerrit.libreoffice.org/59842Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Jenkins
Reviewed-by: Armin Le Grand <Armin.Le.Grand@cib.de>