Add SDO APIs to list, download, and delete public keys

[bmpotter]

• [x] Modify POST /api/keys to be POST /api/orgs/{orgid}/keys
• [x] Add GET /api/orgs/{orgid}/keys that returns the list of public keys
• [x] Add GET /api/orgs/{orgid}/keys/<key-name> that returns the concatenated public key to the user
• [x] Add DELETE /api/orgs/{orgid}/keys/<key-name> that removes the concatenated public key and the associated private key
• [x] Provide org routes for the existing voucher routes:
  • [x] GET /api/orgs/{ord-id}/vouchers/{device-id}
  • [x] GET /api/orgs/{ord-id}/vouchers
  • [x] POST /api/orgs/{ord-id}/vouchers
• [x] Update docs/ocs-api-swagger.yaml accordoingly (and commit to Edge-Fabric/docs too)

[bmpotter]

@dragosguta requested these changes to the keys APIs:

• POST /api/orgs/{orgid}/keys should return 201 http code when successful
• Ensure all APIs set content-type (internally WriteJsonResponse() should set it to application/json)
• Change GET /api/orgs/{orgid}/keys to return:

  [
  {
  "name": "<key-name>",
  "orgid": "<org-id>",
  "owner": "<user>",
  "fileName": "<organization>_<key_name>_public-key.pem",
  "isExpired": false
  },
  ...
  ]

[bmpotter]

Jeff tested these when he add the hzn sub-cmds on top of them.