Use form to construct AtoM upload job arguments
ingest_upload_destination_url_check: use new URL setting
Add new LevelofDescription model

This class is used to track levels of description from an access
system (e.g. AtoM), and is used to tag directories and files when
producing a SIP in order to correctly map items into a DIP.

refs #6980
Add helper to fetch levels of description from AtoM
Add stub for viewing levels of description
Add API to fetch JSON levels of description