Map Border to a gradient stop before the final one.

Map X/YOffset to the focus rectangle of the center shade, i.e. the
opposite of what the import already does.

(cherry picked from commit 82365563)

Conflicts:
	oox/source/export/drawingml.cxx
	sd/qa/unit/import-tests.cxx

Change-Id: I88db7d579da7327e5e06b736a75a6892b338dd73
Reviewed-on: https://gerrit.libreoffice.org/67395Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>