title: TreeView BringIntoView with MVVM
body: <p>I want the user to be able to search for Items in a TreeView.
  After entering a searchtext the TreeViewItem should be scrolled into view.</p>
  
  <p>Right now I am using the MVVM Pattern for the TreeView, for the TreeViewItems and the MainView. </p>
  
  <p>What do I have to do to get the functionality of BringIntoView utilizing MVVM?
  Is there some property I can bind? (in MFC there was something like FirstVisibileItem)</p>
  
  <p>Have seen a "solution" with a behavior. Is it really necessary?</p>