add Event related stuff and Group example

src/main/java/mops/gruppen2/Events/Event.java

@@ -0,0 +1,15 @@
+package mops.gruppen2.Events;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import org.springframework.data.annotation.Id;
+
+@Getter
+@AllArgsConstructor
+public class Event {
+	@Id
+	Long id;
+	Long gruppe_id;
+	Long user_id;
+
+}