refactor(proc. def.): add xml method to the process definition service
refactor(proc. def.): add xml method to the process definition service

lightswitch05/camunda-bpm-sdk-js,nagyistoce/camunda-bpm-sdk-js,camunda/camunda-bpm-sdk-js,nagyistoce/camunda-bpm-sdk-js,camunda/camunda-bpm-sdk-js,lightswitch05/camunda-bpm-sdk-js