Non-unique IDs for tasks in different jobs cause tasks to be overwritten in local DB

This leads to various odd behaviors, like jobs not showing up as "free form" data collection, or jobs having no tasks.

Instead, we should avoid using UUID as PKs in the local db. Instead, we can generate unique numeric IDs, or prevent non-unique IDs in the local DB.

This problem will go away if we serialize the survey as a binary proto in the local db.