title: How to set focus to UserControl (make it selectable)?
body: <p>I need to set focus to <code>UserControl</code> itself, not its child.<br/>
  Otherwise I cannot implement insertion from the buffer. :(<br/>
  Setting <code>Focusable=True</code> doesn't help.
  Google and SO tells only how to set focus to UserControl child.</p>
  
  <p>My control contains:<br/>
   - Toolbar with several buttons bound to commands of the corresponding
     VM<br/>
   - TextBox which is the input for the filter<br/>
   - DataGrid - list of items.<br/></p>
  
  <p>I need to bind Ctrl+V command to VM. But to handle this gesture <code>UserControl</code> must have focus within. When there are no items in the grid (VM's collection is empty) buttons are disabled and the only element which can get focus is <code>TextBox</code>. But it handles Ctrl+V in its own way and I don't want to change this behavior.<br/>
  Thus, I need something to set focus to when I click the area of UserControl.<br/>
  I believe UserControl is the best candidate for it.<br/>
  But I don't know how to make it selectable.</p>