Clean and prepare Archon database before using migration tool

[wickr]

The Archon to ArchivesSpace migration tool gives some ways to check the Archon database to resolve some issues before migrating, or for after a test migration fails.

https://archivesspace.org/wp-content/uploads/2017/12/Archon-to-ArchivesSpace-Migration-Tool-Instructions.pdf

Section A:

• [x] 1. Accession Records - dates and identifiers present
• [x] 2. Classification Records - no duplicate titles
• [x] 3. Collection Records - ran supplied SQL query for normalized dates, 2 collections found, fixed by Kevin
• [x] 4. Level/Container Manager - Kevin added EAD level to Sub-Subseries;
• [ ] 5. Collection Content Records - reviewing, I ran query in 5b looking for references to non-existent IDs but didn't get any results