Added Overview diagram to DBwrench file

Replicating Jeff’s overview diagram for poster.
Removing workflows entities from core schema

The workflows entities had been removed from the ODM2Core diagram, but
had not been removed from the ODM2Core schema.  I removed them, pending
resolution of the workflows issues.  Also - minor change the ODM2Core
diagram where the Observations region had gotten moved out of place.
Update core_actions.md
Resolving merge conflicts so I can merge with master