CreateMETS2: fix conversion of unicode documents into str

Fixes #6767
Transfer start: only suffix components after the first
Remove unused dev-helper-committer

This helper script was never completed, and it doesn't look like there's
much interest in using it.

refs #4757
dev-helper: be less incredulous about transfer backlog
Add PREMIS namespace to Agent

refs #6763

Add PREMIS namespace to PREMIS:AGENT creation in METS.  Minor cleanup.