@NonNull
    public static Single<Response> postJsonRequest(final String uri, final Parameters headers, final Object jsonObject) throws JsonProcessingException {
        final Builder request = new Builder().url(uri).post(RequestBody.create(MEDIA_TYPE_APPLICATION_JSON,
                mapper.writeValueAsString(jsonObject)));
        addHeaders(request, headers, null);
        return RxOkHttpUtils.request(OK_HTTP_CLIENT, request.build());
    }
POST HTTP request with Json POST DATA

@param uri        the URI to request
@param headers    http headers
@param jsonObject the object to be serialized as json and added to the POST request
@return a single with the HTTP response, or an IOException
main/src/main/java/cgeo/geocaching/network/Network.java