title: Caliburn's Screen can not be inherited by Window or UserControl
body: <p>I discovered that Window or UserControl can not inherit Caliburn's Screen base class. Am I forced to implement IScreen interface to every window/user control in my WPF application?  </p>
  
  <pre><code>Imports Caliburn.Micro
  Namespace Views
    Public Class CustomView
      Inherits Screen
    End Class
  End Namespace
  </code></pre>
  
  <blockquote>
    <p>Base class 'Screen' specified for class 'CustomView' cannot be
    different from the base class 'UserControl' of one of its other
    partial types.</p>
  </blockquote>