refaturing message system, step 1: making message abstract and add TranslatableMessage and TranslatedMessage

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

documents/src/main/java/de/srsoftware/umbrella/documents/DocumentApi.java

@@ -577,7 +577,7 @@ public class DocumentApi extends BaseHandler implements DocumentService {
 			LOG.log(WARNING,e);
 		}
 		var attachment = new Attachment(doc.number()+".pdf",rendered.mimeType(),rendered.bytes());
-		var message = new Message(user,new UnTranslatable(subject),new UnTranslatable(content),List.of(attachment));
+		var message = new TranslatedMessage(user,subject,content,List.of(attachment));
 		var envelope = new Envelope(message,new User(doc.customer().shortName(),new EmailAddress(email),doc.customer().language()));
 		postBox().send(envelope);
 		db.save(doc.set(SENT));