Invalid METS export

We noticed some issues with METS exports of digital objects:

• The schema location is not fully referenced. It should be xsi:schemaLocation="http://www.loc.gov/METS/ http://www.loc.gov/standards/mets/mets.xsd"

• metsHdr/@CREATEDATE should be output in ISO 8601 format (e.g., 2019-08-27T09:39:43-04:00 rather than 2019-08-27 09:39:43 -0400)

• Attributes of the type ID and IDREF (e.g., @DMDID, @GROUPID, @FILEID) should be NCNames instead of integers (http://www.datypic.com/sc/xsd/t-xsd_NCName.html)

• FLocat elements are missing @LOCTYPE

This behavior is confirmed in v2.6.0.