Add endfield parameter to Calendar Macro

At this moment the calendar default json service is using startfield and durationfield to compute the enddate of an event. In some cases, the enddate can be provided, so there is no need to compute it again. Also there might be cases when enddate can be provided and durationfield, may not.
The idea is to add the possibilty to use an end date field in the json service, and add also this parameter to the calendar macro.