import part for: "related fdo#45266, don't write extension elements into

... ODF namespaces"

See master commit 88d3931d92bc89519acf95f0510f6f2a6ff7c72c

Change-Id: I8ec31d026f5c6fdc4b7fc573060e7837a337d50b
Signed-off-by: Michael Stahl <mstahl@redhat.com>
(cherry picked from commit 80fc80ae704e3ba3587cde3d146829dc012d29a1)
Reviewed-on: https://gerrit.libreoffice.org/13381
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>