Custom resolver for external v7 draft $ref

Created by: lukeautry

This PR does not need to update the CHANGELOG because it's just a local dev environment thing

Overview

Issue #538 covers the problem. json-schema-to-typescript uses json-schema-ref-parser to normalize and dereference json schemas, but the root schema ref (http://json-schema.org/draft-07/schema) requires making some calls to an external URL, which will always fail for offline devs, or in the case of bad connection, will cause launch.sh to slow down.

Changes

json-schema-ref-parser offers a way to create custom resolvers, which means we can add in custom logic to load the draft 7 schema ref locally.

• json-schema-to-typescript doesn't support passing $RefOptions through dereference in the current version; updated from 5x to 6x
• Created a custom resolver for this case that just reads from a local copy of the v7 draft

fix #538