Summary text in chatlist: Wrong display for adding or deleting members

This is a fix for the add and delete members texts in the chat list: As can be seen from the chat the text is set only once when the object is deserialized, but at this time the sender field is not populated, so we need to do it everytime either sender or content changes. Thats a bit of a copmplicated stuff, but for the moment it is a quick fix. Refactoring though seems necessary.