Use Postgres Views for getting child records and database records

[bennybp]

Description

This migrates to using recursive postgres views in two areas:

1. Finding all direct children of a record, as well as recursively finding all child records of a given record
2. Finding all records for a dataset (both direct and recursively)

This will be faster than what was previously done (although this hasn't been benchmarked). This will also make some planned future queries much easier.

No user-facing API is changed.

Status

• Code base linted
• Ready to go