added URL to ical

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

de.srsoftware.cal.api/src/main/java/de/srsoftware/cal/api/Appointment.java

@@ -39,9 +39,10 @@ public interface Appointment {
 	/**
 	 * represent this event as ical entry
 	 * @param calendarIdentifier used to generate a unique id. pass something that is unique, but stable over time, e.g. a hostname
+	 * @param urlTemplate the url to put into the ical, with "{}" being replaced by the appointment id
 	 * @return the ical string
 	 */
-	String ical(String calendarIdentifier);
+	String ical(String calendarIdentifier,String urlTemplate);
 
 	/**
 	 * ID of the appointment – unique within this system