better handling of anonymous ratings

[epugh]

Description

Motivation and Context

existing cases didn't have a user assigned.. you might also import judgements from someone random, and not have them assigned. this lets you map them so you don't have to rejudge them all if you were that anonymous person ;-)

How Has This Been Tested?

Screenshots or GIFs (if appropriate):

Types of changes

• [] Bug fix (non-breaking change which fixes an issue)
• [] Improvement (non-breaking change which improves existing functionality)
• [] New feature (non-breaking change which adds new functionality)
• [] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [] My code follows the code style of this project.
• [] My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• [] I have read the CONTRIBUTING document.
• [] I have added tests to cover my changes.
• [] All new and existing tests passed.

[epugh]

FYI @david-fisher