Implemented the setting of the received- and read-date of group messages

src/main/java/envoy/data/GroupMessage.java

@@ -43,7 +43,18 @@ public final class GroupMessage extends Message {
 		this.memberStatuses = memberStatuses;
 	}
 
-	public void updateStatus() { setStatus(Collections.min(memberStatuses.values())); }
+	public void updateStatus() {
+		setStatus(Collections.min(memberStatuses.values()));
+		switch (getStatus()) {
+			case RECEIVED:
+				setReceivedDate(new Date());
+				break;
+
+			case READ:
+				setReadDate(new Date());
+				break;
+		}
+	}
 
 	public Map<Long, MessageStatus> getMemberStatuses() { return memberStatuses; }
 }