fdo#63483: support for modify passwd in Impress and Draw

iow, allow opening Impress and Draw ODF documents read-only

Change-Id: I379b9f92b9bfb20e99998177d9a5fae80069d98f
Reviewed-on: https://gerrit.libreoffice.org/11495
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>