Use versioned purl identifiers for dryad-v3.1 crosswalks
XML-encode strings in log entries

Addresses issue reported in https://redmine.dataone.org/issues/3679
Replace remaining instances of http://purl.org/dryad/terms/ with http://purl.org/dryad/schema/terms/v3.1
Merge pull request #233 from datadryad/dan-trello-9

DataONE: namespace versioning and XML-escaping