Implement unique properties

[mike-hogan]

When I have a model, let's say Customer, I want to be able to say that the Email field and the Phone Number field are unique.

These things need to happen:

• [ ] Configure a Property as being unique
• [ ] Have that manifest in the database schema as a unique column
• [ ] Have uniqueness constraint failures on save reported in the data editor, at the offending cell, not just "on the page"

[mike-hogan]

Implemented just now, using an amended upsert_record function that checks unique paths, and uses an advisory lock to ensure atomicity

[mike-hogan]

Implemented just now, using an amended upsert_record function that checks unique paths, and uses an advisory lock to ensure atomicity