replaced appointment.hash by appointment.slug, incooperated slug column into appointments table

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

de.srsoftware.cal.api/build.gradle.kts

@@ -1,5 +1,5 @@
 description = "OpenCloudCal : API"
 
 dependencies {
-    implementation("de.srsoftware:tools.util:1.1.1")
+    implementation("de.srsoftware:tools.util:1.2.1")
 }

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

@@ -34,12 +34,6 @@ public interface Appointment {
 	 */
 	Optional<LocalDateTime> end();
 
-	/**
-	 * create a unique identifier based on the event content
-	 * @return
-	 */
-	String hash();
-
 	/**
 	 * ID of the appointment – unique within this system
 	 * @return the appointment`s id
@@ -53,6 +47,12 @@ public interface Appointment {
 	 */
 	String location();
 
+	/**
+	 * create a unique identifier based on the event content
+	 * @return the slug
+	 */
+	String slug();
+
 	/**
 	 * The date and time, when the appointment starts
 	 * @return the start time as LocalDateTime