Add ContactRelationshipRevealedEvent and address review comments

briar-api/src/org/briarproject/api/privategroup/ContactRelationshipRevealedEvent.java

@@ -0,0 +1,30 @@
+package org.briarproject.api.privategroup;
+
+import org.briarproject.api.event.Event;
+import org.briarproject.api.nullsafety.NotNullByDefault;
+import org.briarproject.api.sync.GroupId;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class ContactRelationshipRevealedEvent extends Event {
+
+	private final GroupId groupId;
+	private final Visibility visibility;
+
+	public ContactRelationshipRevealedEvent(GroupId groupId,
+			Visibility visibility) {
+		this.groupId = groupId;
+		this.visibility = visibility;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+
+	public Visibility getVisibility() {
+		return visibility;
+	}
+
+}