Fixed how POSTs are handled, and PUT/DELETE method

- POST and PUT data was being submitted in the request body, url-
  encoded, with Content-Type: application/json.
  POST, PUT, and DELETE data is now submitted as JSON data in the
  request body.
- POSTs were being queued for an endpoint URL containing an ID.
  The ID was dereferenced from a dict which typically wouldn't
  contain an ID. The Pipedrive server will 500 if the endpoint
  receives an empty ID.
  POSTs now go to an ID-less endpoint URL.