Load a local file of JSON body parts

[talkasab]

• Given JSON file of the form local_codes_eg.json:

[
  { 
      "localCode": { 
          "code": "THX1138", 
          "system": "LOCAL" 
      }, 
      "radlexId": "RID294" 
  }
]

• The local mappings JSON should be able to be added to the constructor of the BodyPartIndex singleton
• When the get or get_by_code methods are called, you can look up cases using the local codes