Use json-schema-merge-allof to merge allOf fields

Created by: ottomata

This allows for schemas to more easily include each other using $ref and allOf. E.g.

allOf:
  - $ref: /path/to/common/schema/1.0.0
  - properties:
      myfieldA:
        type: string
    required:
      - myfieldA

Dereferencing this schema will now also merge everything from the common schema with the properties for this schema, included any required properties.