title: wxPython | wxDataViewListCtrl get all selected rows/items
body: <p>I`m using wxPython in conjunctions with wxFormBuilder.
  I have a wxDataViewListCtrl with 5 columns to list my values.
  The user can select one or more rows (style = wxDV_MULTIPLE).
  If the user only select one row i can catch it with this method:</p>
  
  <pre><code>def showContextTZM( self, event ):
      if self.m_dvlc.HasSelection():
          item_id = event.GetItem().GetID()
  </code></pre>
  
  <p>If the user selects more than one row I only get the item where the cursor is placed.
  I did not find any method to get all selected items.</p>
  
  <p>Thanks for answers.</p>