message: UnknownBody: add explanatory title
diff: @@ -24,7 +24,7 @@ module.exports = React.createClass({
  render: function() {
  const text = this.props.mxEvent.getContent().body;
  return (
  - <span className="mx_UnknownBody">
  + <span className="mx_UnknownBody" title="Redacted or unknown message type">
  {text}
  </span>
  );
  