title: Autosize header in WPF HeaderedItemsControl
body: <p>I'm using a HeaderedItemsControl to show person names. I also want to show a header that contains 3 labels: Title, First Name and Last Name. This is easy when the names are short.
  However, when there is a very long firstname, the header's don't match the names anymore. How can I fix this? Thank you!</p>