Schema centric view

[grantjllnl]

Goal is to make the JSON Observation Schema the central source of truth for data structure. To accomplish this, the final version here will:

1. Generate python data classes. These will replace the existing manually managed classes
2. Generate SQL DDL for base tables
   1. Observations - top level fields
   2. Base Metadata - wide table with fields for all metadata types.
      1. Views for each concrete metadata type with their subset of fields
   3. Signatures - signature data
   4. Certificates - certificate metadata
3. Utilities/helpers will be included for validating the schema and extending it in the future. This can be a tricky and error prone process, so these are intended to ease the pain.
4. A documented process for testing.