[Program Migration] Export/Import Question Validation Predicates

[rockycodes]

We need to import Question Validation Predicates as a part of importing Question Definitions. Question Validation Predicates are tricky to import, however, because ValidationPredicates are already being stored as JSON strings in our database and don't have the "type" field we need to deserialize them into the specific ValidationPredicate class for each question type.

Caitlin outlined three different ways to address this:

1. Perform a database migration
2. Write code to dynamically add the "type" field
3. Write a custom deserializer

See more details in the TDD.